POPULAR 

I/IANUALS 


IC-NRLF 


003 


Importing 


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6 


/A 


HALF-HOUKS  WITH  THE  MICEOSCOPE. 


~-^  ***:  * 


PI. IX 


HALF- HOURS 


THE  MICROSCOPE; 

BEING  A  POPULAR  GUIDE  TO  THE    USE    OF  THE    MICROSCOPE  AS 
MEANS  OF  AMUSEMENT  AND  INSTRUCTION. 


BY    EDWIN    LANKESTER,    M.D. 

ILLUSTEATED  FEOM  NATUEE, 

BY 

TUFFEN   WEST. 

.A.      3ST  IE  "W      IE  X>  I  T  I  O  IsT. 

With  Chapter  on  the  Polwriscope  by  F.  Kitton. 


NEW    YORK  : 

G.    P.    PUTNAM'S    SONS, 

FOUETH     AVENUE    AND    TWENTY-THIED    STEEET. 

1874. 


CONTENTS, 


CHAPTER  J. 

PAGE 
A  HA.LF-HOI7JI  ON  THE  STRUCTURE  OF  THE  MICROSCOPE  1 

CHAPTER  II. 

A  HALF-HOUR  WITH  THE  MICROSCOPE  IN  THE  GARDEN  30 

CHAPTER  III. 

A  HALF-HOUR  WITH  THE  MICROSCOPE  IN  THE  COUNTRY  47 

CHAPTER  IV. 

A  HALF-HOUR  WITH  THE  MICROSCOPE  AT  THE  POND- SIDE          $6    % 

CHAPTER  Y. 

A  HALF-HOUR  WITH  THE  MISCROSCOPE  AT  THE  SEA-SIDE          6?     , 

CHAPTER  VI. 

A  IIALT-.HOUR  WITH  THE  MICROSCOPE  IN-DOORS  78 

CHAPTER  VII. 

A  HAIF-HOUR  WITH  POLARIZED  LIGHT 


APPENDIX. 

THE  PREPARATION  AND  MOUNTING  OF  OLJECTS 

I  2 


DESCRIPTION  OF   PLATES. 


In  the  examination  of  these  Plates  the  observer  is 
requested  to  remember  that  they  are  not  all  drawn  to 
the  same  scale.  Some  objects,  adapted  for  low  powers, 
are  only  magnified  a  few  times,  whilst  smaller  objects 
are  magnified  many  Jiundred  times.  All  objects,  of 
course,  vary  in  apparent  size,  according  to  the  powers 
with  which  they  are  examined.  Descriptions  of  the 
objects  will  be  found  in  the  pages  indicated. 


PLATE  I.  to  face  page  1. 
FIO.  PAGE 

1.  Vegetable  cells  with,  nucleus  from  apple 31 

2.  'Cellular  tissue  from  pith  of  elder    31 

3.  Stellate  cell-tissue  from  rush    32 

4.  Flat  tabular  cell  from  surface  of  tongxie 91 

5.  Ciliated  cell  from  windpipe  of  calf ?1 

€.  Human  blood  corpuscles   91 

7.  Blood  corpuscles  from  fowl    92 

8.  Blood  corpuscle  from  frog 92 

9.  Blood  corpuscle  from  sole ,  92 

10.  Blood  corpuscle  from  beetle 92 

11.  Filament  of  a  species  of  Zygnema,  a  plant 60 

a.  Portion  of  a  filament  of  the  same,  the  cell- 
contents  becoming  changed  into  zoospores. 
&,  Zoospore  more  highly  magnified. 


X  THE   MICROSCOPE. 

FJO,  PAGE 

12.  Filament  of  a  species  of  OsciUatoria,  a  plant    ....  60 

a.  Portion  more  highly  magnified. 

]  3.  Pandorlna  Morum,  a  plant 60 

14.  Volvox  Globator,  a  plant 60 

15.  Englena  viridis,  a  plant,    showing   various   forms 

which  it  assumes    61 

18o  Amoeba,  an  infusory  animalcule 69 

a,  b,  c,  show  the  various  forms  which  thi-3  ani- 
malcule assumes 

17.  Actinoplirys  Sol,  the  sun  animalcule 62-60 

18.  Difflugia,  an  infusory  animalcule 63 

19.  Arcella,  an  infusory  animalcule    , 63 

20.  Lagena,  a  species  of  Foraminifer 69 

21.  Polystomella  crispa,  a  species  of  Foraminifer 69 

22.  Gldbigerina,  a  species  of  Foraminifer 69 

23.  Rosalina,  from  chalk,  a  Foraminifer    69 

24.  Living  Rosalina,  a  Foraminifer    C9 

25.  Texlilaria,  a  species  of  Foraminifer QQ 


PLATE  II.  to  face  page  32. 

26.  Uha  in  different  stages  of  development , , .,    gj 

a.  Cells  in  single  series. 

J.  Commencement  of  lateral  extension. 

c.  Portion  expanded. 

27    Cosrnarium,  a  species  of    Desmid  undergoing  self- 
division. 

28.  Eaaslrum,  a  species  cf  Desmid 57 

29.  Closterium,  a  species  of  Desmid « .  t    57 

a.  Undergoing  self-division. 
£0.  D&midium,  a  species  of  Desmid v ...    57 


DESCRIPTION   OF  PLATE3.  xi 

FIG.  PAGE 

31.  Pediastrum,  a  species  of  Desmid 57 

32.  Scencdcsmus,  a  species  of  Desmid , . . . .  57 

S3.  Surlrella  nobilis,  a  species  of  Diatom 59 

34.  Pinnularia  viridis,  a  species  of  Diatom 59 

35.  a.  Navicula,  a  species  of  Diatom  undergoing  self- 

division 
&.  Front  view  of  the  same. 

36.  Melosira  varians,  a  species  of  Diatom 59 

37.  Melosira  nummuloides  undergoing  self-division   . ...  59 

38.  Coscinodiscus  eccentricus,  a  species  of  Diatom 58 

39.  Paramecium  Aurelia,  an  iufusory  animalcule 64 

40.  Vorticella  nebulifera,  an  infusory  animalcule 63 

41.  Rotifer  vulgaris,  a  wheel  animalcule 65 

42.  Stomates  on  a  portion  of  cuticle  of  hyacinth  leaf   ..  32 

43.  Sinuous  walled  cells  and  stomates  from  under  sur- 

face of  leaf  of  water-cress    32 

44.  Cuticle  of  wheat  straw  with  stomates 33 

45.  Cuticle  from  petal  of  geranium  (Pelargonium). ...  33 

46.  Cuticle  from  leaf  of  a  species  of  aloe 33 

47.  Spiral  vessel  from  leaf-stalk  of  garden  rhubarb ....  35 

48.  Ditto  unrolled 35 

49.  Annular  vessel  from  wheat  root 35 

50.  Dichotomous  spiral  vessels    35 

51.  Dotted  duct  from  common  radish     * . . .  35 

52.  Scalariform  tissue  from  fern  root 35 

53.  Woody  fibre  from  eider.. «%... « 35 


THE   MICROSCOPE. 


PLATE  III.  to  face  page  40. 
FIG.  PAGE 

54.  "Glandular"  woody  tissue   34 

55.  Transverse  section  of  glandular  woody  tissue    ....  3-1 

56.  Transverse  section  of  oak 34 

57.  Long  section  of  oak 34 

58.  Oblique  section  of  oak 34 

59.  Section  of  cork , 35 

60.  Transverse  section  of  coal 36 

61.  Longitudinal  section  of  coal 36 

62.  Wheat  starch 37 

63.  Oat  starch    37 

64.  Potato  starch 37 

65.  Tous-les-mois  starch 37 

66.  Indian  corn  starch 38 

67.  Sago  starch -. 37 

68.  Tapioca  starch    37 

69.  Acicular  raphides  from  garden  hyacinth 38 

70.  Bundle  of  ditto  from  leaf  of  aloe  contained  in  a  cell  33 

71.  Compound  raphides  from  stalk  of  garden  rhubarb. .  39 

72.  Tabular  prismatic  raphides  from  outer  coat  of  onion  39 

73.  Circular  crystalline  mass  from  a  cactus 39 

74.  Simple  vegetable  hair  from  leaf  of  a  common  grass  40 

75.  Rudimentary  hair  from  flower  of  pansy 40 

76.  Simple  club-shaped  hair, 40 

77.  Club-shaped  hair  from  leaf  of  dock 41 

78.  Hair  from  throat  of  pansy 40 

79.  a.  Hair  formed  of  two  cells  from  flower  of  white 

dead-nettle 41 

79,  6.  Many-jointed   tapering    hair   with    nuclei    from 

common  groundsel ..,-., »...  4] 


DESCRIPTION   OF   PLATES.  xiii 

PTO,  PAGE 

SO.  Beaded  hair  of  sow-thistle 41 

81.  Glandular  hair  from  leaf  of  common  tobacco 41 

82.  Hair  from  leaf  of  garden  chrysanthemum 41 

83.  Rosette-shaped  glandular  hair  from  flower  of  verbena  41 

84.  Stellate  hairs  from  the  hollyhock  (A Ithasa  rosea)..  41 

85.  a.  Stellate  hair  from  leaf  of  lavender 41 

85,  6.  Hair  from  leaf  of  garden  verbena,  with  warty 

surface 45 

86.  Hair  from  leaf  of  white  poplar  (Populus  alba)  ....  41 

87.  Ease  of  a  hair  on  a  mass  of  cellular  tissue 41 

88,  a.  A  sting  from  common  nettle 42 

88,  6.  Portion  of  a  leaf  of  Valisneria 42 


PLATE  IV.  to  face  page  48. 

89.  Palmclla  cruenta — gory  dew 48 

90.  Yeast  plant 48 

91.  Portions  of  vinegar  plant    48 

92.  So-called  cholera  fungus  obtained  from  the  air. ...  48 

93.  Red  rust  of  wheat    49 

94.  Puccinia  yraminis — mildew    49 

95.  Pent  till  him  glaucum — common  mould 49 

96.  Boirytis  from  mouldy  grape    49 

,     97.  Fungus  from  mouldy  bread  (Mucor  Muccdo]    ....  49 

98.  Fungus  from  human  ear 49 

99.  Fungus  from  leaf  of  bramble  (Phragmidium  bul- 

I'osum) 49 

100.  Vine  blight  (Oldium  Tuckeri) 50 

101.  Potato  blight  (Bolrylis  infcslans)    50 

102.  a.  Pea. blight  (Erysiplie  Pisi)  50 

6.  Asci  and  sporidia  of  pea  blight CO 

103.  Fungus  from  a  decayed  Spanish  nut 50 


XIV  THE   MICROSCOPE, 

FIG.  PAGE 

104.  Curious  fungus  from  oil  casks    50 

105.  Fungus  of  common  ringworm  (Achorion  Schonlenii)    50 

106.  Fungus  on  stem  of  duckweed 50 

a.  Another  within  the  cells. 

107.  a.  Branched  cells  from  stem  of  mushroom 51 

I.  Branched  cells  from  rootlets  of  mushroom    ....     51 
C.  Reproductive  bodies  borne  ra  fours  on  the  gills 

of  mushrooms 51 

108.  Section  through  a  brilliant  orange-coloured  peziza    52 

109.  Section  through  the  common  yellow  lichen  of  trees 

and  walls 52 

110.  Leaf  of  Sphagnum — bog  moss     52 

111.  Sea  weed — Polyslphonia  fastiyiata 67 

a.  Fruit-bearing  organs. 
&.  Spore. 

c.  Portion  of  Bispore ;  and 

d.  „         Tetraspore. 

e.  Antheridia. 

112.  Eeproductive  organs  of  a  moss,  a  species  of  Tortula    52 

a.  The  calyptra. 
6.  The  operculum. 

c.  The  peristome. 

d.  The  teeth. 

e.  The  spores. 

113.  Fructification  on  back  of  frond  of  male  fern. .....     53 

114.  Fructification  on  back  of  frond  of  common  brakes    53 

115.  Capsules    of  Scolopendrium  —  hartstongue.      The 

sporules  seen  escaping 53 

a.  One  of  the  latter  more  magnified 53 

116.  Fructification  of  Equisetum — horsetail  ..........     55 

a.  Shield-like  disk  of  ditto,  separated,  surrounded 
by  thecffl 55 


DESCRIPTION   OF   PLATES.  XV 


FIG. 

116,  6.  Spore,  much  magnified,  with  elastic  filaments 

coiled  closely  round  ......................     55 

c.  Spore  expanded    ..........................      55 

117,  a.  Fructification  of  Lycopodium  —  club  moss  ......     54 

b.  Sporules    ....................  .  ....  .......     54 

C.  Sporules  more  highly  magnified, 


PLATE  V.  to  face  page  56. 

118.  Delicate  spiral  cells  from  anthers  of  furze 44 

119.  Large  well-developed  spiral  cells  from  anthers  of 

hyacinth,  with  minute  raphides  in  intercellular 

spaces 44 

120.  Irregular  deposit  in  cells  of  anthers  of  white  dead- 

nettle  44 

121.  Annular  ducts  from  anthers  of  narcissus 44. 

122.  Stellate  cells  from  anthers  of  crown  imperial   ....  44 

123.  Ovate  pollen  cells 44 

124.  Triangular  pollen  cells  from  hazel 44 

125.  Pollen  cells  of  heath    44 

126.  Pollen  cells  of  dandelion 44 

127.  Pollen  cells  of  passion  flower 45 

128.  Pollen  cells  of  mallow 45 

129.  Eed  poppy  seed 46 

130.  Black  mustard  seed 46 

131.  Seed  with  deep  and  curved  furrows •  46 

132.  Great  snapdragon  seed    *  46 

133.  Chickweed  seed 41 

134.  Umbelliferous  seed  or  fruit     ••  46 

135.  Zygnema,  conjugating 60- 

136.  Clostenum,  conjugating • »  57 


XV]'  THE    MICROSCOPE. 

FHJ.  PAGE 

137.  Cosmarlum,  conjugating .....,,*  57 

138.  Epiiheiiiia  gibbet,  conjugating 43 

2 39.  Melosira  nummuloidcs,  conjugating   59 

110.  Transverse  section  of  common  sponge 6} 

141.  Transverse  section  of  common  British  sponge  ....  63 

a.  Spicules  of  the  same  more  magnified. 

Calcareous  spicules  of  Grantia  ciliufa.  68 

142.  Pin-like  spiculum  from  Cliona,  a  boring  sponge  . .  69 

143.  Spiculum  from  Spongilla,  a  fresh-water  sponge  . .  69 

144.  Spiculum  from  unknown  sponge    69 

145.  Spiculum  from  Tethea f>9 

146.  Common  Hydra   70 

a.  Stinging  organ  from  common  Hydra 

147.  A  species  of  Sertularia,  a  zoophyte    71 

148.  Campanularia  Integra,  a  zoophyte 71 

149.  "  Cup"  of  Campanularia  volubilis,  a  zoophyte. ...  71 

1 50.  Spicula  of  Gorgonia  verrucosa 71 

151.  Transverse  section  from  base  of  spine  of  Echinus 

neglectus 72 

152.  Calcareous  rosette  from  sucker  of  Echinus    72 

153.  Pedicellaria  from  Echinus   72 

154.  Pedicellaria  from  star-fish 72 


PLATE  VI.  to  face  page  72. 

155.  Lepralia,  a  polyzoon »  72 

156.  BoicerbanTcia  densa,  a  polyzoon 73 

157.  Tobacco-pipe,  or  bird's-head  processes  of  Notamia  73 

a.  Bird's-heau  process. 

158.  Bugula  avicularia 73 

159.  Bird  's-head  process  of  Bugula  Murrayana    .   «•«»  73 


DESCRIPTION   OF   PLATES.  XVU 

FIG.  PAGE 

160.  Scrupularia  swuposa,  with   bird's-head  processes 

(avicularia)  and  sweeping  bristles  (vibracula). .  73 

161.  Snake-headed  zoophyte — Anyuinaria 73 

162.  Flustra  foliacea — sea  mat   72 

163.  Plumatdla  repens,  a  fresh-water  polyzoon 74 

164.  Egg  of  Cristatella  Muccdo,  a  fresh-water  polyzoon  74 

165.  Transverse   section    of   shell   of    Pinna,  showing 

prismatic  shell  structure 74 

166.  Longitudinal  section  of  shell  of  Pinna 75 

167.  Transverse  section  from  oyster-shell 7  ft 

168.  Section  of  shell  of  Anomia,  with  tubular  borings. .  75 

169.  Section  of  mother  of  pearl 75 

170.  Prawn-shell  viewed  as  a  transparent  object 75 

171.  Teeth  of  whelk 73 

172.  Teeth  of  limpet 75 

173.  Teeth  of  periwinkle 73 

174.  Teeth  of  Limneus 75 

175.  Scale  of  sturgeon — ganoid 7^ 

176.  Prickle  from  back  of  skate — placoid 7« 

177.  Borings  by  a  minute  parasite  in  a  fossil  fish-scale. .  ^7 

178.  Scale  of  sole — ctenoid »* 

179.  Scale-,  "whiting — cycloid 77 

a.  CuL-^eous  particles,  magnified. 

180.  Scale  of  sprat — cycloid 7V 

181.  Section  of  egg-shell 90 

182.  From  soft  egg. 

183.  Section  of  egg-shell  of  emu 90 


PLATE  VI  I.  to  face  page  80. 

184.  Human  hair , . . ,      78 

a*  Transverse  section  of  human  hair. 


XV111  THE   MICROSCOPE. 

FIG.  PAGE 

185,  a.  Small  mouse-hair......,,., , 79 

6.  Larger  mouse-hair. 

c.  Plain  mouse-hair. 

d.  Minute  hair  from  ear  of  mouse. 

136.  Hair  of  long-eared  bat 50 

187.  Transverse  section  of  hair  of  peccary   80 

183.  Pith-like  hair  of  musk-deer SO 

1S9.  Hair  from  tiger  caterpillar  . , So 

190.  a.  Branched    hairs    from    leg   of    garden   spider 

(Epeira  diadema)    81 

b.  Spine,  with  spiral  flutings,  from  the  same. 

C.  Small    brush-Lite    hairs    from    an   Australian 

spider. 

191 .  Hair  from  flabellum  of  crab    81 

192.  Portion  of  four  of  the  barbs  of  a  goose-quill 81 

193.  Portion  of  the  same  more  magnified 81 

194.  Swan's-down 81 

195.  Head  and  mouth  of  a  flea    82 

196.  Head  and  mouth  of  a  bug 82 

197.  Mandible  of  humble  bee Si 

198.  Head  and  mouth  of  louse    §3 

199.  Head  and  mouth  of  gnat . .  83 

200.  Extremities  of  barbs  of  the  sting  of  common  bee. .  34 

201.  Head  of  honey  bee    83 

a.  Piece  of  the  tongue  more  magnified. 

202.  Mouth  of  blow-fly    84 

203.  Head  and  mouth  of  butterfly 84 

204.  One  of  the  fangs  of  a  spider,  showing  the  poison- 

bag  and  duct 85 

205.  Foot  of  Empis,  a  species  of  fly   87 

206.  Foot  of  bee    87 

207.  Foot  of  spider  87 


DESCRIPTION   OF   TLATES. 


FIG. 

208.  Head  of  common  spider,  showing  eight  simple  eyes. 

a.  Cornea  of  one  of  these  more  magnified 85 

209.  Skin  of  garden  spider 85 

210.  Portion  of  compound  eye  of  fly 83 

211.  Portions  of  the  two  wings  of  bee  in  flight 88 

a.  Nervule  of  wing. 

212.  Spiracle  of  fly 86 

213.  Spiracle  of  Dytiscus 86 

214.  Threads  of  garden  spider  (Epeira  diadema) 86 

Simple  thread  of  the  same. 

Thread  of  a  concentric  circle  with  viscous  dots. 

PLATE  VIII.  to  face  page  88. 

215.  Fore  leg  of  Gyrinus  natator,  whirligig  beetle   ....     87 

216.  Middle  leg  of  the  same    87 

217.  Hind  leg  of  same 87 

218.  Fore  leg  of  male  Dytiscus  87 

219.  Middle  leg  of  the  same. 

220.  a.  Gizzard  of  cockroach    89 

6.  Ditto,  cut  open. 

221.  a.  Gizzard  of  cricket    89 

&.  Ditto,  cut  open. 

222.  Trachea  from  caterpillar 86 

223.  Proleg  of  caterpillar   of   common   garden    white 

butterfly,  with  the  membranes  in   which  the 

hooks  are  seated,  expanded  as  in  action 83 

224.  Part  of  leg  of  cockroach 

225.  Battledore  scale  from  blue  argus  butterfly    88 

226.  Scale  of  ordinary  shape  from  same 88 

227.  Scale  from  meadow-brown  butterfly 88 

228.  Scaleofgnat .33 


XX  THE   MICROSCOPE. 

PIG.  PAGE 

229.  Scale  reduced  to  a  hair  from  clothes-moth 85 

230.  Hair-like    scale    from    clothes-moth,   with    three 

prongs 89 

231.  Cartilage  from  mouse's  ear 91 

232.  Transverse  section  of  human  bone 90 

233.  Striped  muscular  fibre  from  meat 92 

234.  a.  Liber  fibre  of  flay,  natural  state    , . . . .  79 

b.  Ditto,  broken  across  at  short  intervals 

235.  Wool  from  flannel 79 

236.  Silk ., 79 

237.  Cotton  hair 79 

238.  Crystal  of  honey f;l> 

239.  Thick  crystal  of  ordinary  sugar — same  angles  ....  39 

240.  Crystals  of  sugar  from  adulterated  honey 40 

241.  Cuticle  from  berry  of  holly 35 

242.  Transverse  section  of  whalebone    90 

243.  Transverse  section  of  plum-stone 31 

244.  Transverse  section  of  testa  of  seed  of  Guelder  rose  13 

245.  Fruit  of  groundsel — opaque   42 

246.  One  hair  of  pappus  of  dandelion 42 

247.  Cottony  hair  of  burdock 42 

248.  Portion  of  pappus  of  goats-beard 42 

249.  "Wood  of  young  shoots  of  vine,  the  cells  containing 

starch S3 

250.  Spiral  fibres  from  testa  of  wild  sage  seed 35 

PLATE  IX.     Frontispiece  to  face  title-page. 

1.  lodo-sulphate  of  Quinine 

2.  Salicine 

3.  Aspartic  Acid 

4.  Sulphate  of  Copper  in  Gelatine 

5.  Grey  Hair  (human) 

6.  Scales  of  Hyppophas  rhainnoides 


VrWestimp. 


Robert  Eandwicke  ,1860 


HALF-HOURS  WITH  THE  MICROSCOPE, 


CHAPTER     I . 

A   HALF-HOUE    ON   THE   STEUCTUEE    OF  THE 
MICEOSCOPE. 

THE  Microscope  is  often  regarded  merely  as  a 
toy,  capable  of  affording  only  a  certain  amount  of 
amusement.  However  much  this  might  have  been 
the  case  when  its  manufacture  was  less  perfectly 
understood,  it  is  now  an  instrument  of  so  much 
importance  that  scarcely  any  other  can  vie  with 
it  in  the  interest  we  attach  to  the  discoveries  made 
by  its  aid.  By  its  means  man  increases  the  power 
of  his  vision,  so  that  he  thus  gains  a  greater  know- 
ledge of  the  nature  of  all  objects  by  which  he  is 
surrounded.  What  eyes  would  be  to  the  man  who 
is  born  blind,  the  Microscope  is  to  the  man  who 
sees  only  with  his  naked  eye.  It  opens  a  new 
world  to  him,  and  thousands  of  objects  whose  form 
and  shape,  and  even  existence,  he  could  only  ima- 
gine, can  now  be  observed  with  accuracy. 

Nor  is  this  increase  of  knowledge  without  great 
advantages.  Take  for  instance  the  study  of  plants 
and  animals.  Both  are  endowed  with  what  we 
call  life  :  they  grow  and  perform  certain  living 
functions  ;  but  as  to  the  mode  of  their  growth,  and 
the  way  in  which  their  functions  were  performed, 
little  or  nothing  was  known  till  the  Microscope 
revealed  their  minute  structure,  and  showed  fe^\N  v 
thei*-  Carious  parts  were  related  to  each  other.  The 
B 


2  THE    STRUCTURE    OF 

Microscope  has  thus  become  a  necessary  instrument 
in  the  hands  of  the  botanist,  the  physiologist,  the 
zoologist,  the  anatomist,  and  the  geologist. 

Let  us.  then,  endeavour  to  understand  how  it  is 
this  little  instrument  has  been  of  such  great  service 
in  helping  on  the  advancement  of  science.  Its  use 
depends  entirely  on  its  assisting  the  human  eye  to 
see — to  see  more  with  its  aid  than  it  could  possibly 
do  without  it.  This  it  does  by  enabling  the  eye  to 
be  brought  more  closely  in  contact  with  an  object 
than  it  otherwise  could  be. 

Just  in  proportion  as  we  bring  our  eyes  close  to 
objects,  do  we  see  more  of  them.  Thus,  if  we  look 
at  a  printed  bill  from  the  opposite  side  of  a  street, 
we  can  see  the  larger  letters  only ;  but  if  we  go 
nearer  we  see  the  smaller  letters,  till  at  last  we  get 
to  a  point  when  we  can  see  no  more  by  getting 
closer.  Now  suppose  there  were  letters  printed  on 
the  bill  so  small  that  we  could  not  see  them  with 
the  naked  eye,  yet,  by  the  aid  of  a  lens — a  piece  of 
convex  glass — we  could  bring  our  eyes  nearer  to 
the  letters,  and  see  them  distinctly.  It  would  depend 
entirely  on  the  form  of  the  lens,  as  to  how  close  we 
could  bring  our  eyes  to  the  print,  and  see;  but  this 
great  fact  will  be  observed,  that  the  nearer  we  can 
get  our  eyes  to  the  print,  the  more  we  shall  see. 
The  most  important  part  of  a  Microscope,  then, 
consists  of  a  lens,  by  means  of  which  the  eye  can 
be  brought  nearer  to  any  object,  and  is  thus  enabled 
to  see  more  of  it.  Magnifying-glasses  and  Simple 
Microscopes  consist  mainly  of  this  one  element. 
In  order,  however,  to  enable  the  eye  to  get  as  close 
as  possible  to  an  object,  it  becomes  convenient  to 
use  more  than  one  lens  in  a  glass  through  which  we 
look.  These  lenses,  for  the  sake  of  convenience, 
are  fixed  in  a  brass  frame,  and  attached  to  the 
Simple  Microscope ;  when  there  are  two  lenses  they 


THE   MICROSCOPE.  3 

are  called  doublets,  and  when  three  they  are  termed 
triplets.  The  magnify  ing-glasses  which  are  made 
to  be  held  in  the  hand,  frequently  have  two  or 
three  lenses,  by  which  their  power  may  be  increased 
or  decreased.  Such  instruments  as  these  were  the 
first  which  were  employed  by  microscopic  observers: 
and  it  is  a  proof  of  the  essential  nature  of  this 
part  of  the  Microscope,  that  many  of  the  greatest 
discoveries  have  been  made  with  the  Simple  Mi- 
croscope. 

The  nearer  the  glass  or  lens  is  brought  to  an 
object,  so  as  to  enable  the  eye  to  &ee,  the  more  of 
its  details  will  be  observed.  So  that  when  we  use 
a  glass  which  enables  us  to  see  within  one  inch  of 
an  object,  we  see  much  more  than  if  we  could  bring 
it  within  only  an  inch  and  a  half  or  two  inches. 
So  on,  till  we  come  to  distances  so  small  as  the 
eighth,  sixteenth,  or  even  twentieth  of  an  inch. 

Although  a  great  deal  may  be  seen  by  a  common 
hand-glass,  such  as  may  be  purchased  at  an  optician's 
for  a  few  shillings,  yet  the  hand  is  unsteady ;  and 
if  these  glasses  were  made  with  a  very  short  focus, 
it  would  be  almost  impossible  to  use  them.  Besides, 
it  is  very  desirable,  in  examining  objects,  to  have 
both  hands  free.  On  these  accounts  the  glasses, 
which  in  such  an  arrangement  are  called  object- 
glasses  (see  fig.  3),  are  attached  to  a  stand,  and  placed 
in  an  arm,  which  moves  up  and  down  with  rack- 
work.  Tn  this  way,  the  distance  of  the  object  from 
the  glass  can  be  regulated  with  great  nicety.  Under- 
neath the  glass,  and  attached  to  the  same  stand,  is 
a  little  plate  or  framework,  to  hold  objects,  which 
are  placed  on  a  slide  of  glass.  This  is  called  the 
stage.  (Fig.  1,  G.)  Sometimes  rack-work  is  added  to 
this  stage,  by  which  the  objects  can  be  moved  upon 
it  backwards  and  forwards,  without  being  moved 
by  the  hand.  Such  an  arrangement  as  this  is 
B  2 


4:  THE   STRUCTURE    OF 

called  a  Simple  Microscope.  Of  course  many  other 
things  maybe  added  to  it,  to  make  it  more  conveni- 
ent for  observation  ;  but  these  are  its  essential  parts. 
But,  although  the  Simple  Microscope  embraces 
the  essential  conditions  of  all  Microscopes,  and  has, 
in  the  hands  of  competent  observers,  done  so  much 
for  science,  it  is,  nevertheless,  going  out  of  fashion, 
and  giving  way  to  the  Compound  Microscope.  (Fig.  1, 
p.  5.)  This  instrument,  as  might  be  inferred  from  its 
name,  is  much  more  complicated  than  the  Simple 
Microscope,  but  it  is  now  constructed  with  so  much 
accuracy,  that  it  can  be  used  with  as  great  cer- 
tainty and  ease  as  the  Simple  Microscope  itself.  In 
order  to  understand  the  mechanism  of  the  Compound 
Microscope  we  must  first  of  all  study  the  principles 
on  which  it  is  constructed.  If  we  take  a  common 
convex  lens  and  place  any  small  object  on  one  side 
of  it,  so  as  to  be  in  its  focus,  and  then  place  on  the 
other  side  a  sheet  of  white  paper,  we  shall  find  at 
a  certain  point  that  an  enlarged  picture  of  the 
object  will  be  produced  on  the  paper ;  and  this  is 
the  way  in  which  pictures  are  formed  by  the 
camera  of  which  the  photographic  artist  avails 
himself  for  his  portraits  and  sun-pictures.  Now  L 
we  look  at  this  picture  with  another  lens  of  the 
same  character  but  of  somewhat  less  magnifying 
power,  we  shall  obtain  a  second  picture  larger  than 
the  first,  and  this  is  the  principle  involved  in  the 
Compound  Microscope.  The  superiority  of  this 
instrument  over  the  Simple  Microscope  consists  in 
an  increase  of  magnifying  power.  There  is,  how- 
ever, a  limit  to  the  utility  of  this  magnifying  power ; 
for  when  objects  are  greatly  magnified  they  become 
indistinct.  This  is  seen  in  the  Oxyhydrogen  and 
Solar  Microscopes,  where  the  images  are  thrown,  by 
means  of  highly  magnifying  lenses,  on  a  white  sheet; 
and,  although  made  enormously  large,  their  details 


THE    MICROSCOPE.  5 

are  much  less  clear  than  when  looked  at  by  a  lens 
magnifying  much  less.     Another  advantage  of  the 


Fig.  1  * 
Compound  Microscope. 

Compound  Microscope  is  the  distance  at  which  the 
eye  is  placed  from  the  object,  and  the  facility  with 

*  In  this  little  work  we  have  purposely  abstained  from 
mentioning  either  the  names  or  the  Microscopes  of  our 
principal  makers,  lest  we  should  thereby  seem  to  give  a 


6  THE    STRUCTURE    OF 

wLich  the  hands  may  be  used  for  all  purposes  of 
manipulation. 

A  brief  description,  aided  by  the  accompanying 
illustration,  will,  it  is  hoped,  suffice  to  make  the 
beginner  acquainted  with  the  various  parts  of  this 
important  instrument. 

We  have  already  mentioned  that  when  powerful 
lenses  are  used  in  the  examination  of  small  objects 
the  hand  is  not  sufficiently  steady  to  give  a  firm 
support  to  the  lens  employed,  and  this  is  equally 
true  of  the  hand  that  holds  the  object.  It  is  also 
essentially  requisite  to  have  both  hands  free,  for 
the  purpose  of  manipulation.  Hence  it  becomes 
necessary  to  devise  some  mechanical  means  for  the 
support  of  both  the  lens  and  the  object.  How 
these  wants  have  been  supplied  by  the  enterprising 
skill  and  ingenuity  of  our  opticians  will  be  best 
seen  as  we  describe  the  various  parts  of  which  the 
Compound  Microscope  consists. 

The  most  important  part  of  the  instrument  is 
undoubtedly  that  which  carries  the  various  lenses 
or  magnifying  powers.  These  are  contained  in  the 
interior  of  the  tube  or  body,  A,  which  is  usually 
constructed  of  brass,  and  from  8  to  10  inches  in 
length.  At  the  upper  end  of  the  tube  is  the  eye- 
piece, B,  so  named  from  its  proximity  to  the  eye  of 
the  observer.  It  consists  of  two  plano-convex 
lenses,  set  in  a  short  piece  of  tubing,  with  their 
flat  surfaces  turned  towards  the  eye,  and  at  a 
distance  from  each  other  of  half  their  united  focal 
lengths.  The  first  of  these  lenses  is  the  eye-glass, 
while  that  nearest  the  objective  is  termed  the  field 
lens.  The  use  of  the  latter  is  to  alter  the  course 

preference  to  any.  The  general  excellence  of  these  instru- 
ments is  so  well  known  and  the  names  of  their  makers  are 
so  universal  that  the  student  will  find  no  difficulty  in  provid- 
ing himself  with  an  efficient  instrument  at  a  moderate  cost. 


THE    MICROSCOPE. 


of  the  light's  rays  in  their  passage  to  the  eye,  in 
such  manner  as  to  bring  the  image  formed  by  the 
object-glass  into  a  condition  to  be  seen  by  the  eye- 
glass. A  stop  also  is  placed  between  the  two  lenses 
in  such  a  position  that  all  the  outer  rays,  which  pro- 
duce the  greatest  amount  of  distortion,  arising  from 
spherical  and  chromatic  aberration,  are  cut  off.  The 
short  tube  carrying  the  lenses  (fig.  2)  slides  freely, 
but  without  looseness,  into  the  upper  end  of  the  com- 
pound body,  A,  an  arrangement  which  affords  a  ready 
and  convenient  method  for  changing  the  eye-pieoe. 

Compound  Microscopes 
are  generally  fitted  up 
with  two  eye-pieces,  the 
one  deep  and  the  other 
shallow.  The  last  has  its 
lenses  close  together,  and 
magnifies  the  most,  whilst 
the  other  has  them  far- 
ther apart,  and  magnifies 
less.  In  the  use  of  these 
eye-pieces,  it  should  never 
be  forgotten  that  the  one 
which  magnifies  least  is 
generally  the  most  trust- 
worthy. 


Fig.  2.     Eye-piece. 


At  the  opposite  end  of  the  tube  A  is  the  object- 
glass  C.  The  use  of  this  lens  is  to  collect  and 
bring  to  a  point  the  rays  of  light  that  proceed 
from  any  object  placed  in  its  focus.  At  this  point 
an  enlarged  image  of  the  object  will  be  formed  in 
the  focus  of  the  eye-glass.  We  have  only  to  look 
through  the  latter  at  the  picture  thus  formed  in 
order  to  obtain  a  second  image  larger  than  the 
first.  And  this  is  the  way  in  which  minute  objects 
are  made  to  appear  so  much  larger  than  when  seen 
by  the  unassisted  eye.  It  will  at  once  be  seen  how 


8  THE   STRUCTURE    OP 

much  of  the  utility  of  a  Microscope  depends  on 
good  object-glasses.  Where  they  are  faulty,  the 
image  they  form  is  also  faulty ;  and  when  these 
faults  in  the  first  image  are  multiplied  by  the 
power  of  the  eye-piece,  they  become — like  the  faults 
of  our  friends  when  viewed  through  a  similar 
medium — of  great  magnitude. 

A  good  object-glass  may  be  known  by  its  giving 
a  clear  and  well-defined  view  of  any  object  we  may 
wish  to  examine  ;  while  a  bad  lens  may  be  equally 
well  known  by  the  absence  of  these  qualities.  In 
short,  a  badly  constructed  objective  is  more  apt  to 
mislead  than  to  guide  the  student,  by  the  fictitious 
appearances  it  creates — appearances  that  may  be 
erroneously  taken  for  realities,  which  have  no  exist- 
ence in  the  object  itself.  The  object-glasses  of  our 

best  opticians  consist  of  several 

lenses  arranged  in  pairs,  set  in  a 
small  brass  tube.  A  screw  at 
one  end  serves  to  attach  them 
to  the  lower  extremity  of  the 
compound  body,  A.  (Fig.  3.) 
The  body  of  the  Microscope  is 
supported  by  a  stout  metal  arm, 
D,  into  the  free  end  of  which  it 
screws.  The  opposite  end  of  the 
arm  is  secured  to  the  stem,  E, 
by  a  screw,  on  which  it  moves 

Fig.  3.  Object-Glass.  af  on   a   Pivot«      B7  this  means 
the  tube  of  the  Microscope  can 

be  turned  away  from  the  stage — an  arrangement 
that  gives  this  form  of  Microscope  an  advantage 
over  those  that  are  not  so  constructed.  To  the 
stem,  J£,  which  works  up  and  down  a  hollow  pillar 
by  rack-work  and  pinion,  is  attached  the  stage,  G. 
This,  in  its  simplest  form,  consists  of  a  thin  flat 
plate  of  brass,  for  holding  objects  undergoing  ex- 


THE    MICROSCOPE.  9 

animation.  In  the  centre  is  a  circular  opening,  for 
the  passage  of  the  light  reflected  upward  by  the 
mirror,  H.  There  is  also  a  sliding  ledge,  //  against 
this  the  glass  slide,  on  which  the  object  is  mounted, 
rests,  when  the  Microscope  is  inclined  from  the 
perpendicular. 

In  a  stage  of  this  kind  the  various  parts  of  an 
object  can  only  be  brought  under  the  eye  by 
shifting  the  slide  with  the  fingers.  But  in  more 
expensive  instruments  the  stage  is  usually  con- 
structed of  one  or  two  sliding  plates,  to  which 
motion  is  given  by  rackwork  and  pinion ;  the 
whole  being  brought  under  the  hand  of  the  operator 
by  two  milled  heads,  a  mechanical  arrangement 
which  enables  him  to  move  with  ease  and  certainty 
the  object  he  may  wish  to  investigate. 

Underneath  the  stage 
is  the  diaphragm,  K,  a 
contrivance  for  limiting 
the  amount  of  light 
supplied  by  the  mirror, 
H.  It  consists  of  a 
thin,  circular,  flat  plate 
of  metal,  turning  on  a 
pivot,  and  perforated 
with  three  or  four  cir- 
cular holes  of  varying 
diameter  (fig.  ^  4),  the  Diaphragm. 

largest  only  being  equal 

to  the  aperture  in  the  stage.  By  turning  the  plate 
round,  a  succession  of  smaller  openings  is  brought 
into  the  centre  of  the  stage,  and  in  one  position  of 
the  diaphragm  the  light  is  totally  excluded.  By 
this  small  but  useful  contrivance  the  Microscopist 
can  adjust  the  illumination  of  the  mirror  to  suit 
the  character  of  the  object  he  may  be  investiga- 
ting. In  some  Microscopes  the  diaphragm  is  a  fix- 


10  THE   STRUCTURE    OF 

ture,  but  in  the  better  class  of  instruments  it  is 
simply  attached  to 
the  under  part  of 
the  stage  by  a  bayo- 
net catch,  or  by  a 
sliding  plate  of  me- 
tal (fig.  5),  and  can 
be  readily  removed  pig.  5.  Diaphragm, 

therefrom    when    it 

is  desirable   to   employ   other  methods  of  illumi- 
nation. 

In  working  with  the  Microscope  it  is  necessary 
to  adopt  some-  artificial  means  for  ensuring  a  larger 
supply  of  light  than  can  be  obtained  from  the 
natural  diffused  light  of  day,  or  from  a  lamp  or 
candle.  For  this  purpose  the  Microscope  is  fur- 
nished with  a  double  mirror,  H,  having  two  reflect- 
ing surfaces,  the  one  plane  and  the  other  convex. 
The  latter  is  the  one  usually  employed  in  the  illu- 
mination of  transparent  objects ;  the  rays  of  light 
which  are  reflected  from  its  concave  surface  are 
made  to  converge,  and  thus  pass  through  the  object 
in  a  condensed  form  to  the  eye.  The  plane  mirror 
is  used  generally  in  conjunction  with  an  achromatic 
condenser,  when  parallel  rays  only  are  required. 
The  whole  apparatus  is  attached  to  that  portion  of 
the  hollow  pillar  continued  beneath  the  stage,  in 
such  a  manner  that  it  can  be  moved  freely  up  and 
down  the  stem  that  supports  it.  This  motion 
enables  the  Microscopist  to  regulate  the  intensity 
of  his  light  by  increasing  or  decreasing  the  distance 
between  the  mirror  and  the  stage ;  while  the 
peculiar  way  in  which  the  mirror  itself  is  suspended 
on  two  points  of  a  crescent-shaped  arm,  turning  on 
a  pivot,  gives  an  almost  universal  motion  to  the 
reflecting  surfaces.  The  observer  by  this  means 
can  secure  any  degree  of  oblique  illumination  ha 


THE   MICROSCOPE.  11 

may  require  for  the  elucidation  of   the  structure 
undergoing  examination. 

We  next  come  to  the  stand,  which,  though  the 
most  mechanical,  is  at  the  same  time  a  very  impor- 
tant part  of  the  Compound  Microscope.  On  the 
solidity  and  steadiness  of  this  portion  of  the  instru- 
ment depends  in  a  great  measure  its  utility.  The 
form  generally  adhered  to  is  that  represented  in  our 
diagram  (fig.  1,  p.  5.)  It  consists  of  a  tripod  base,  P, 
from  which  rise  two  flat  upright  pillars,  0.  Between 
these,  on  the  two  hinge-joints  shown  at  L,  is  sus- 
pended the  whole  of  the  apparatus  already  described  : 
namely,  the  body  carrying  the  lenses,  the  arm  to 
which  it  is  attached,  the  stage,  and  the  mirror 
underneath  it.  By  this  contrivance  the  Microscope 
can  be  inclined  at  any  angle  between  a  vertical  and 
horizontal  position — an  advantage  which  can  be  duly 
appreciated  by  those  who  work  with  the  instrument 
for  two  or  three  hours  at  a  time.  Close  to  the 
points  of  suspension  are  the  milled  heads,  M ;  these 
are  connected  with  a  pinion  working  in  a  rack  cut 
in  the  stem,  E.  By  turning  the  milled  heads  the 
tube  is  made  to  approach  or  recede  from  the  stage 
until  the  proper  focus  of  the  object-glass  is  found. 
This  is  termed  the  coarse  adjustment,  and  is  gene- 
rally used  for  low  powers,  where  delicate  focussing  is 
not  required.  But  when  high  magnifying  powers 
are  used,  that  require  a  far  greater  degree  of  pre- 
cision, we  have  recourse  to  the  fine  adjustment,  N, 
which  consists  of  a  screw  acting  on  the  end  of  a 
lever.  The  head  of  the  screw  by  which  motion  ic 
communicated  to  the  object-glass  is  divided  into  ten 
equal  parts,  and  when  caused  to  rotate  through  any 
of  its  divisions  slightly  raises  or  depresses  the  tube, 
carrying  the  objective  with  it.  As  the  screw  itself 
contains  just  150  threads  to  an  inch  one  revolution 
of  its  head  will  cause  an  alteration  of  the  150th 


12  THE    STRUCTURE    OF 

of  an  inch  in  the  distance  of  the  lens  from  the 
object.  When  moved  through  only  one  of  its 
divisions  we  obtain  a  result  equal  to  the  1500th  of 
an  inch,  and  by  causing  it  to  rotate  through  half  a 
division  we  secure  a  movement  not  exceeding  the 
3000th  part  of  an  inch  in  extent.  Such  nicety  in 
the  adjustment  of  the  optical  part  of  the  Micro- 
scope may  seem  to  the  beginner  unnecessary,  but 
when  he  comes  to  work  with  high  powers  he  will 
find  that  he  needs  the  most  delicate  mechanical 
contrivances  to  enable  him  to  secure  the  proper 
focus  of  a  sensitive  object-glass. 

But  this  is  not  the  only  use  to  which  we  can  put  the 
fine  adjustment.  The  same  process  that  serves  to  re- 
gulate the  focus  of  a  lens  will  also  enable  us  to  measure 
pretty  accurately  the  thickness  of  an  object  or  any 
of  the  small  prominences  or  depressions  found  in  its 
structure.  By  observing  the  number  of  divisions 
through  which  the  head  of  the  screw  is  made  to 
pass  while  changing  the  focus  of  the  object-glass 
from  the  bottom  to  the  top  of  any  small  cavity  or 
prominence  we  get  a  tolerable  notion  of  its  depth 
or  height,  &c.  Connected  with  this  apparatus  is  a 
special  contrivance  for  protecting  the  object-glass 
to  some  extent  from  injury.  It  will  sometimes 
happen,  even  with  the  most  careful,  when  using 
high  powers,  that  the  lens  is  brought  down  with 
some  force  in  contact  with  the  glass  cover  that 
protects  the  object.  This  risk  is  not  unfrequently 
incurred  by  admitting  to  one's  study  incautious 
friends,  whose  confidence  is  only  equalled  by  their 
ignorance ;  who  although  they  may  have  never  seen  a 
Microscope  before,  will  proceed  to  turn  it  up  and 
down  with  a  force  sufficient  to  crack  the  lens. 
Such  friends  would  have  sufficient  confidence  in 
themselves  to  take  the  command  of  a  man-of-war, 
even  though  it  were  the  first  time  in  their  lives 


THE    MICROSCOPE,  13 

they  Lad  been  on  board  a  ship.  Strict  injunctions 
must  be  laid  on  all  such  not  to  approach  the  table 
until  the  instrument  is  quite  ready  for  them  to  take 
a  peep,  coupled  with  a  polite  request  that  while 
doing  so  they  will  keep  their  hands  behind  them. 
A  provision  has  been  made  which  to  some  extent 
provides  for  such  an  emergency.  The  object-glass 
itself  is  screwed  into  a  short  tube,  that  fits  accu- 
rately the  lower  end  of  the  compound  body  and 
slides  freely  within  it,  being  kept  down  in  its  place 
by  a  spiral  spring,  which  presses  upon  it  from 
behind.  On  the  application .  of  a  slight  force  or 
resistance  to  the  object-glass  the  spring  tube 
immediately  yields,  within  certain  limits,  to  the 
pressure,  carrying  with  it  the  lens,  which  is  thus 
often  saved  from  destruction.  Object-glasses  of 
various  degrees  of  magnifying  power  and  excellence 
of  workmanship  are  supplied  with  th-e  Microscope, 
and  may  be  purchased  separately,  according  to  the 
wants  and  resources  of  the  student.  It  will  be 
found  that  for  all  ordinary  purposes  the  1-inch  and 
1-inch  objectives  are  the  most  useful  powers.  A 
substitute  for  the  intermediate  powers  may  be 
obtained  by  pulling  out  the  draw-tube  and  using 
the  higher  eye-pieces.  This  method,  though  not  so 
satisfactory  in  its  results  as  the  use  of  separate 
object-glasses,  may  be  resorted  to  where  a  series 
of  objectives  are  not  within  the  reach  of  the 
observer. 

THE   BINOCULAR   MICROSCOPE. 

Since  the  invention  of  the  Stereoscope  attempts 
have  been  made  to  apply  the  Binocular  principle 
in  the  construction  of  the  Compound  Micro- 
scope. After  some  failures  this  desideratum  has 
been  successfully  achieved  by  Mr.  F.  H.  "Wenham, 
a  gentleman  well  known  to  microscopists  by 


14:  THE    STRUCTURE    O¥ 

the  fertility  of  his  resources  and  the  ingenuity  of 
his  inventions  in  connection  with  the  Microscope. 
It  is  to  him  that  we  are  indebted  for  a  Microscope 
that  enables  us  to  see  objects  in  a  natural  manner, 
namely,  with  both  eyes  at  once.  Hitherto  the 
ordinary  single-tubed  Microscope  reduced  the  ob- 
server to  the  condition  of  a  Cyclops.  Although 
gifted  with  a  pair  of  eyes  he  found  it  impossible  to 
avail  himself  of  this  plurality  of  organs.  He  was 
condemned  by  the  very  nature  of  his  Microscope 
to  peer  perpetually  with  a  single  eye  through  its 
solitary  tube  ;  but  thanks  to-  Mr.  Wenham  all  this 
is  changed.  We  have  now  the  satisfaction  of  using 
a  double-tubed  Microscope  that  not  only  gives  em- 
ployment to  both  eyes  at  once,  but  presents  us  with 
effects  unknown  and  unattainable  by  the  ordinary 
instrument.  We  no  longer  gaze  at  a  flat  surface, 
but  a  stereoscopic  image  stands  out  before  us  with 
a  boldness  and  solidity  perfectly  marvellous  to  those 
who  have  only  been  accustomed  to  the  ordinary 
single-tubed  Microscope. 

"  No  one,"  says  a  writer  in  '  The  Popular  Science 
He  view,'  "  can  fail  to  be  struck  with  the  beautiful 
appearance  of  objects  viewed  under  the  Binocular 
Microscope.  Its  chief  application  is  to  such  objects 
as  require  low  powers,  and  can  be  seen  by  reflected 
light,  when  the  wonderful  relief  and  solidity  of  the 
bodies  under  observation  astonish  and  delight  even 
the  adept.  Foraminifera,  always  beautiful,  have 
their  beauties  increased  tenfold  ;  vegetable  struc- 
tures, pollen,  and  a  thousand  other  things,  are  seen 
in  their  true  lights,  and  even  diatoms,  we  may  pre- 
dict, will  receive  elucidation,  as  to  the  vexed  ques- 
tions of  the  convexity  or  concavity  of  their  infinitely 
minute  markings.  The  importance  of  the  Binocular 
principle  is  especially  apparent  when  applied  to 
anatomical  investigation.  Prepared  Microscopic 


TIIE    MICROSCOPE. 


injections  exhibit  under  the  ordinary  Microscope  a 
mass  of  interlacing  vessels,  whose  relation,  being 
all  on  the  same  plane,  it  is  not  easy  to  make  out 
with  any  degree  of  satisfaction.  But  placed  under 
the  Binocular  they  at  once  assume  their  relative 
position.  Instead  of  a  flat  band  of  vessels,  we  now 
see  layer  above  layer  of  tissue  ;  deeper  vessels  an- 
astomosing with  those  more  superficial ;  the  larger 
vessels  sending  branches,  some  forward  and  some 
backward,  and  the  whole  injection  assumes  its 
natural  appearance,  instead  of  being  only  like  a 
picture" 

Fortunately  for  the  possessors  of  the  ordinary 
Microscope,  the  Bin- 
ocular arrangement 
can  be  readily  adapted 
to  this  instrument  at 
a  cost  of  a  few- 
pounds.  The  addi- 
tional tube  and  prism 
does  not  interfere 
with  the  use  of  the 
instrument  as  a  mon- 
ocular, the  withdrawal 
of  the  prism  instantly 
converts  it  into  that 
form  of  instrument : 
this  is  necessary  when 
high  powers  are 
used. 

The    accompanying 
diagram    (fig.    6)  —  a 
section    of    the    Bin- 
ocular —  will      give  * 
the   reader   a  correct           Fig.  6.    Section  of 
notion  of  the  mecha-         Binocular  Microscope. 


16  THE    STRUCTUKE   OF 

nism  of  the  instrument.  Let  G  represent  the  body 
of  the  ordinary  Microscope  and  £  the  secondary 
tube  attached  to  the  side  of  the  former,  which  it 
will  be  seen  has  a  portion  of  its  surface  cut  away 
at  the  point  of  junction,  F,  as  a  means  of  commu- 
nication between  them.  The  eye-pieces  and  draw- 
tubes  are  seen  at  D  and  E.  The  object-glass  G 
is  attached  to  the  ordinary  tube  C  in  the  usual 
way.  Just  above  it  is  the  small  prism,  A, 
mounted  in  a  brass  box,  and  so  constructed  as 
to  slide  into  an  opening  in  the  tube  at  the  back 
of  the  object-glass.  By  this  arrangement  it  will 
be  found  that  while  one  half  of  the  light  passes  up  the 
tube  unobstructed  the  other  half  must  first  pass 
through  the  prism,  where, 
after  undergoing  two  re- 
flections (fig.  7),  it  es- 
capes in  the  direction  of 
the  additional  tube  B.  The 
dotted  lines  in  the  diagram 
show  the  direction  the 
light  takes  in  its  passage 
to  the  eyes.  At  H  the  rays 
are  seen  to  cross  each  other. 
Those  from  the  left  side  of 
the  obj  ect-glass  traverse  the 
.  _  right  tube,  while  those  from 

Double-reflecting  Prism.     ^   rigbt'side  of  the   lens 

are  projected  up  the  left  tube. 

In  using  the  Binocular  it  must  be  remembered 
that  the  eyes  of  different  individuals  vary  in  their 
distance  from  each  other.  It  will  thus  be  seen 
that  some  contrivance  is  necessary  to  enable  us  to 
increase  or  decrease  the  distance  between  the  eye- 
pieces to  suit  the  requirements  of  all.  This  is 
accomplished  by  the  two  draw-tubes,  D  and  E, 
which  carry  the  eye-pieces.  When  drawn  out,  the 


THE    MICROSCOPE.  IT 

latter  are  made  to  diverge,  and  when  pushed  iu 
they  converge.  In  this  way  any  intermediate 
distance  can  be  obtained  to  suit  every  kind  of 
vision. 

"Where  a  Binocular  Microscope  is  in  daily  use  it 
will  sometimes  be  necessary  to  withdraw  the  prism 
from  the  tube,  to  cleanse  it  from  dust  and  other 
impurities  gradually  contracted  by  use.  Whenever 
this  may  be  necessary  great  care  should  be  taken 
to  employ  no  substance  likely  to  scratch  its  highly 
polished  surfaces;  for  on  these  being  preserved  intact 
in  a  great  measure  depends  the  efficiency  of  the  in- 
strument. We  know  of  nothing  better  adapted  for 
removing  impurities  than  a  clean  silk  or  cambric 
handkerchief,  which,  when  not  in  use,  should  be  kept 
in  a  closely-fitting  drawer,  to  protect  it  from  dust. 

There  seems  to  be  little  doubt  that  this  lately 
improved  form  of  the  Compound  Microscope  will 
eventually  supersede  all  others.  This  opinion  also 
seems  to  be  entertained  by  the  inventor  himself, 
whose  words  we  quote  : — 

"  The  numerous  Microscopes  that  have  been 
altered  into  Binoculars,  in  accordance  with  my  last 
principle,  and  also  the  large  quantity  still  in  the 
course  of  manufacture,  will,  I  think,  justify  me  in 
making  the  assertion,  without  presumption,  that 
henceforth  no  first-class  Microscope  will  be  con- 
sidered complete  unless  adapted  with  the  Binocular 
arrangement." 

The  Compound  Microscope  is  now,  undoubtedly, 
one  of  the  most  perfect  instruments  invented  and 
used  by  man.  In  the  case  of  all  other  instruments, 
the  materials  with  which  they  are  made  and  the 
defects  of  construction  are  drawbacks  on  their  per- 
fect working  ;  but  in  the  Compound  Microscope 
we  have  an  instrument  working  up  to  the  theory 
of  its  construction.  It  does  actually  all  that  could 
c 


18  THE    STRUCTURE   OF 

be  expected  from  it,  upon  a  correct  theory  of  the 
principles  upon  which  it  is  constructed.  Neverthe- 
less, this  instrument  did  not  come  perfect  from  its 
inventor's  hands.  Its  principles  were  understood  by 
the  earlier  microscopic  observers  in  the  seventeenth 
and  eighteenth  centuries,  but  there  were  certain 
drawbacks  to  its  use,  which  were  not  overcome  till 
the  commencement  of  the  second  quarter  of  the 
present  century. 

These  drawbacks  depended  on  the  nature  of  the 
lenses  used  in  its  construction.  The  technical  term 
for  the  defects  alluded  to  are  chromatic  and  spheri- 
cal aberration.  Most  persons  are  acquainted  with 
the  fact  that,  when  light  passes  through  irregular 
pieces  of  cut  glass — as  the  drops  of  a  chandelier, — 
a  variety  of  colours  is  produced.  These  colours, 
when  formed  by  a  prism,  produce  a  coloured  image 
called  the  spectrum.  Now,  all  pieces  of  glass 
with  irregular  surfaces  produce,  more  or  less,  the 
colours  of  the  spectrum  when  light  passes  through 
them  j  and  this  is  the  case  with  the  lenses  which 
are  used  as  object-glasses  for  Microscopes.  In 
glasses  of  defective  construction,  every  object 
looked  at  through  them  is  coloured  by  the  agency 
of  this  property.  The  greater  the  number  of 
lenses  used  in  a  Microscope,  the  greater,  of  course, 
is  the  liability  to  this  colouring.  This  is  chromatic 
aberration ;  and  the  liability  to  it  in  the  earlier- 
made  Compound  Microscopes  was  so  great  that  it 
destroyed  the  value  of  the  instrument  for  purposes 
of  observation. 

Again,  the  rays  of  light,  when  passing  through 
convex  lenses,  do  not  fall — when  they  form  a 
picture — all  on  the  same  plane;  and  therefore, 
instead  of  forming  the  object  as  presented,  pro- 
duce a  picture  of  it  that  is  bent  and  more  or  less 
distorted.  This  is  spherical  aberration,  and  a  fault 


THE   MICROSCOPE.  19 

which  was  liable  to  be  increased  by  the  number  of 
glasses,  in  the  same  way  as  chromatic  aberration. 
This  defect  also  is  increased  in  Compound  Micro- 
scopes ;  and  formerly,  the  two  things  operated  so 
greatly  to  the  prejudice  of  this  instrument  that  it 
was  seldom  or  never  used. 

Gradually,  however,  means  of  improvement  were 
discovered.  These  defects  were  rectified  in  tele- 
scopes; and  at  last  a  solution  of  all  the  difficulties 
that  beset  the  path  of  the  Microscope-maker  was 
afforded  by  the  discoveries  of  Mr.  Joseph  Jackson 
Lister,  a  gentleman  engaged  in  business  in  London, 
who,  in  a  paper  published  in  the  Philosophical 
Transactions  for  1829,  pointed  out  the  way  in 
which  the  Compound  Microscope  could  be  con- 
structed free  from  chromatic  and  spherical  aberra- 
tion. This  is  done  by  such  an  arrangement  of  the 
lenses  in  the  object-glass,  that  one  lens  corrects  the 
defects  of  the  other.  Thus,  in  object-glasses  of  the 
highest  power,  as  many  as  eight  distinct  lenses  are 
combined.  We  have,  first,  a  triplet,  composed  of 
two  plano-convex  lenses  of  crown-glass,  with  a 
plano-concave  of  flint-glass  between  them.  Above 
this  is  placed  a  doublet,  consisting  of  a  double 
convex  lens  of  crown,  and  a  double  concave  one  of 
flint-glass.  At  the  back  of  this  is  a  triplet,  which 
consists  of  two  double  convex  lenses  of  crown- 
glass,  and  a  double  concave  one  of  flint  placed  be- 
tween them.  Such  are  the  combinations  necessary 
to  correct  the  defects  of  lenses  when  employed  in 
Compound  Microscopes. 

It  is  this  instrument,  then,  which  is  most  com- 
monly employed  at  the  present  day,  and  to  which 
we  are  indebted  for  most  of  the  recent  progress  in 
microscopic  observation. 

In  using  the  Microscope,  a  great  variety  of  acces- 
sory apparatus  may  be  employed  to  facilitate  the 
c  2 


20 


THE    STRUCTURE    OF 


various  objects  which  the  observer  has  in  vievr. 
As  this  is  a  book  for  beginners,  w<;  shall  only 
mention  a  few  of  these. 

Microscopes  are  generally  supplied  with  small 
slips  of  glass,  three  inches  long  and  one  inch  wide. 
These  are  intended  to  place  the  objects  on  which 
are  to  be  examined.  They  are  cither  used  tempo- 
rarily or  permanently  with  this  object  in  view, 


Fig.  8.     Forceps. 

and  are  called  slides.     When  used  temporarily,  an 
object,  such  as  a  small  insect,  or  part  of  an   insect, 


Fig.   9.     Bull's-eye  Condenser. 

is  placed  upon  the  middle  of  it  ;  and  it  may  be 
either  placed  immediately  upon  the  stage  at  the 


THE    MICROSCOPE,  21 

proper  distance  from  the  object-glass,  or  a  drop 
of  water  may  be  placed  on  the  slide,  and  a  piece 
of  thinner  glass  placed  over  the  object.  This  is 
the  most  convenient  arrangement,  as  you  may 
then  tilt  your  Microscope  without  the  slide  or 
object  falling  off. 

Objects,  when  placed  under  the  Microscope,  are 
of  t\vo  kinds — either  transparent  or  opaque.  When 
they  are  opaque,  they  may  either  be  placed  upon 
the  slips  of  glass,  or  put  between  a  small  pair  of 
forceps  (tig.  8),  which  are  fixed  to  the  stage  of  the 
Microscope,  and  the  light  of  a  window  or  lamp 
allowed  to  fall  upon  them.  This  is  not,  however, 
sufficient,  generally,  to  examine  things  with  great 
accuracy ;  and  an  instrument  called  a  condenser 
(tig.  9)  is  provided  for  this  purpose.  It  consists 
merely  of  a  large  lens,  which  is  sometimes  fixed  to 
the  stage,  or  has  a  separate  stand.  Its  object  is  to 
allow  a  concentrated  ray  of  light  to  be  thrown  on 
the  opaque  object  whilst  under  the  object-glass  of 
the  Microscope.  This  is  called  viewing  objects  by 
reflected  light. 

Transparent  objects,  *>n  the  other  hand,  are 
viewed  by  transmitted  light,  reflected  from  the 
plane  or  concave  surface  of  the  mirror  beneath  the 
stage.  The  object  of  this  mirror,  which  is  called 
the  re/lector,  is  to  caU«h  the  rays  of  light  and  con- 
centrate them  on  the  object  under  the  Microscope^ 
The  rays  of  light  thus  pass  through  the  object,  and 
its  parts  are  sesii  much  more  clearly. 

Another  convenient  piece  of  apparatus  is  an 
animalcule  cage.  This  consists  of  a  little  brass  box, 
inverted,  to  the  bottom  of  which  is  attached  a 
piece  of  glass.  Over  this,  again,  is  placed  a  lid 
or  cover,  with  a  glass  top.  The  cover  can  be  made 
to  press  on  the  glass  beneath,  and  an  object  being 
placed  between  the  two  glasses,  can  be  submitted 


22  THE   STRUCTURE    OF 

to  any  amount  of  pressure  thought  necessary, 
(Fig.  10.)  This  is  a  very  important  instrument 
for  examining  minute  Crustacea,  animalcules, 
zoophytes,  and  other  living  and  moving  objects, 
especially  when  they  live  in  water. 


Fig.  10.      Animalcule  Cage  or  Live  Box. 

In  the  use  of  the  cage  and  the  slide,  care  must 
be  taken  not  to  break  them  by  turning  the  object- 
glass  down  upon  them.  It  is  sometimes  a  difficult 
thing,  when  the  object-glass  has  a  focus  of  not 
more  than  a  quarter  or  eighth  of  an  inch,  to  adjust 
it  to  exactly  the  point  at  which  the  object  is  best 
seen,  by  means  of  the  coarse  handles  on  the  rack- 
work.  For  this  reason  the  Microscope  has  been 
provided  with  a  fine  adjustment,  by  which  the 
object-glass  is  moved  down  on  the  object  in  a 
much  slower  and  more  gradual  manner,  and  the 
destruction  of  an  expensive  objective  glass  is  often 
thus  prevented. 

The  picture  of  the  object  brought  to  the  eye  in 
the  Compound  Microscope  is  always  the  wrong  end 
upwards.  That  is,  the  picture  is  always  the  reverse 
in  the  Microscope  to  what  it  is  with  the  naked  eye. 
You  need  constantly  to  be  aware  of  this,  especially 
if  you  are  going  to  dissect  an  object  under  the 
Microscope,  as  your  right  hand  becomes  left,  and 
your  left  right.  The  observer,  however,  soon  gets 
accustomed  to  this,  and  it  creates  no  difficulty  ulti- 
mately. But  science  constantly  attends  on  the 


THE    MICROSCOPE. 


23 


Microscope,  and  ministers  to  its  slightest  defects. 
A  little  instrument  called  an  erector,  composed  of 
a  lens  which  reverses  the  picture  once  more,  is 
supplied  by  the  optician,  and  can  be  had  by 
those  who  practise  the  refinements  of  microscopic 
observation. 

It  is  a  good  plan  to  make  drawings  of  all  objects 
examined,  or  at  any  rate  those  which  are  new  to 
the  observer.  A  note-book  should  be  kept  for  this 
purpose,  and  what  cannot  at  once  be  identified  by 
the  object,  may  afterwards  be  so  by  the  drawing. 
All  persons,  however,  have  not  the  gift  of  drawing, 
and  for  those  who  need  assistance  in  this  way,  the 
camera  lucida  has  been  invented.  This  instrument 
is  applied  to  the  tube  of  the  Microscope  when  placed 
at  right  angles  with 
the  stem,  in  such  a 
way  that  a  person 
looking  into  it  sees 
the  object  directly 
under  his  eye,  so  that 
he  may  easily  draw 
its  form  on  a  piece 
of  paper  placed  un- 
derneath. (Fig.  11.) 
Some  little  practice 
is,  however,  necessary 
before  the  observer 
can  obtain  satisfac- 
tory results  with  this 
instrument.  It  is 
absolutely  essential 
that  the  eye  should 
be  so  placed  that, 
while  one  part  of  the 


Fig.  II.     Camera  Lucida. 


pupil  receives  the  rays  from  the  reflecting  surface 


24  THE    C'i'AUCTURE    OF 

of  the  prism,  the  other  sees  the  paper  below  with 
the  image  clearly  depicted  upon  it.  Dr.  Beale 
strongly  recommends  the  neutral  lens  glass 
reflector  in  preference  to  the  Wollaston  camera 
lucida.  It  is  also  much  less  costly.  (Fig.  HA.) 
This  consists  of  a  short  tube  falling 
upon  the  eye-piece,  with  a  piece  of 
neutral  lens  glass  placed  at  such  an 
angle  that,  whilst  the  image  of  the 
object  is  reflected  upwards,  the  paper 
below  can  be  distinctly  seen.  (The 
price  of  this  form  of  camera  lucida  is 
about  four  or  five  shillings.)  Success 
in  the  use  of  the  camera  depends  very 
Fig.  HA.  much  on  the  arrangement  of  the  light. 
If  the  image  is  too  strongly  illuminated, 
the  paper  will  hardly  be  visible ;  and,  on  the 
contrary,  if  the  paper  and  pencil  are  too  bright, 
the  image  is  indistinct.  A  little  practice  will 
enable  the  observer  to  overcome  both  difficulties  : 
this  he  will  have  attained  when  he  can  see  the 
image  and  paper  with  equal  distinctness. 

Another  instrument  which  will  be  found  of  con- 
siderable service  even  to  the  beginner  with  the 
Microscope,  is  a  micrometer'  This  is  an  instrument 
for  measuring  the  size  of  objects  observed.  Exag- 
gerated notions  about  the  smallness  of  objects  arc 
very  prevalent  j  and  as  it  is  almost  impossible  to 
say  accurately  how  small  an  object  is  without  some 
means  of  measuring,  a  Micrometer  becomes  essen- 
tial where  accuracy  is  desired.  This  is  effected  by 
having  some  object  of  known  size  to  compare  with 
the  object  observed.  The  most  convenient  instru- 
ment of  this  kind  is  a  glass  slide,  on  which  lines 
are  drawn  the  hundredth  and  thousandth  of  an 
inch  apart.  If  this  slide,  or  stage  micrometer  as  it 
is  called,  is  placed  on  the  stage,,  the  divisions  may 


THE   MICROSCOPE.  Z.O 

be  traced  on  the  paper  in  the  same  way  as  the 
outline  of  an  object :  the  dimensions  of  the  latter  can 
now  be  ascertained.  Care  must,  however,  be  taken 
that  the  magnifying  power  is  the  same  in  both  cases. 

Amongst  the  accessory  apparatus  are  various 
arrangements  for  concentrating  the  light  en  the 
objects  which  are  placed  for  examination  under 
the  Microscope.  One  of  these  combinations  is 
called  the  achromatic  condenser.  This  consists  of 
a  series  of  lenses,  which  are  placed  between  the 
mirror  and  the  stage,  and  which  may  consist  of 
an  ordinary  object-glass.  The  stages  of  the  larger 
kinds  of  Microscopes  are  fitted  up  with  a  screw  or 
slide,  by  which  the  condenser  can  be  fastened 
beneath  and  adjusted  to  the  proper  focus  for 
throwing  light  on  the  object  examined. 

The  illumination  of  opaque  objects  by  means  of 
the  bull's-eye  condenser  is  sufficient  when  only  the 
lowest  powers  are  used  ;  but  when  any  objective  of 
less  than  inch-and-half  focus  is  used  this  method  of 
illumination  is  not  satisfactory,  and  a  form  of 
reflector  called  a  Lieberkiihn  will  be  found  to  be  a 
welcome  addition  to  the  Microscope.  This  instru- 
ment consists  of  a  concave  silvered  speculum  with 
a  central  aperture  of  the  diameter  of  the  front  lens 
of  the  objective  :  a  short  tube  is  attached  to  the 
convex  surface  of  the  reflector,  which  slides  over 
the  object-glass.  The  action  of  the  Lieberkiihn  will 
be  easily  understood  from  the  following  diagram  : 
a  represents  the  objective  with  the  LielerJcilhn  in 
situ ;  6,  the  concave  reflector  j  c,  a  stop  for  the 
purpose  of  preventing  any  direct  light  entering  the 
objective  (a  small  disk  of  black  paper  attached  to 
the  slide  is  generally  sufficient) ;  d,  d,  rays  of  light 
from  the  mirror  ;  e,  e,  reflected  rays  converging  to 
a  focus  at  f  (the  object).  To  obtain  the  full 
effect  of  this  mode  of  illumination  the  mirror  should 


THE    STRUCTURE    OF 


be  placed  a  little  out  of  the  axis  of  the  tube  of  the 
Microscope.  By  this  method  an  oblique  beam  of 
light  is  thrown  on  the  Lieberkuhn,  and  the  light 
from  it  is  reflected  unequally  upon  the  object ;  thus 
producing  the  light  and  shade  so  necessary  for  the 
proper  definition  of  an  object.  (The  cost  of  a 
Lieberkuhn  varies  from  6s.  to  15s.  ;  those  for  low 
powers  costing  more  than  those  for  the  higher.) 

The  details  of  many 
transparent  objects 
are  much  more  dis- 
tinctly seen  when 
examined  by  light 
transmitted  by  the 
object  only.  This  is 
called  black  ground 
illumination,  and  can 
be  obtained  in  several 
ways.  With  a  very 
low  power  the  light 
can  be  reflected  with 
sufficient  obliquity  if 
the  mirror  is  thrown 
out  of  the  axis  ;  but 
much  better  effects 
Fig.  llB.  Diagram  illustrating  are  obtained  when  a 
the  action  of  a  «• Lieberkiihn."  hemispherical  lens 
a,  omect-glasg  ;  o.  a  concave  -.i  1111 

silver 'reflector  ;  c,  a  black  spot  Wlth  a  cenlral  black 
("dark  well") ;  d,  d,  rays  of  light;  stop,  called  a  "  spot 
e,  e,  the  same  reflected  and  lens,"  is  placed  be- 
brought  to  a  focus  at/.  neath  the  object.  The 

accompanying  figure  will  explain  its  action  : — 
a  is  "  spot  lens " ;  b,  a  brass  tube  in  which 
it  is  mounted  (this  is  fitted  into  a  larger  tube 
fitted  to  the  short  tube  attached  to  the  lower 
surface  of  the  stage  :  by  sliding  this  up  or  down,  the 
proper  distance  from  the  object  is  obtained) ;  c, 


THE   MICROSCOPE. 


parallel  lines  from  mirror ;  d,  the  same  rays  made 
to  rapidly  converge  by  passing  through  the  lens, 
and  come  to  a  focus  at  e  j  and  if  the  focal  length 
of  the  objective  is  greater  than  the  distance  between 
the  object  and  the  point  e,  the  object  will  be  illu- 
minated, and  the  field  appear  perfectly  dark. 


Kg.  lie. 

a,  "  Spot  Lens,"  front  view ;  c,  blackened  concavity  of 
ditto  ;  a',  section  of  "  Spot  Lens  "  in  its  fitting,  b  ;  c',  central 
stop  ;  d  d,  parallel  rays  of  light  converging  to  a  focus  at  e. 

Having  said  thus  much  with  regard  to  apparatus, 
we  will  now  give  some  directions  for  the  use  of 
the  Microscope  under  ordinary  circumstances.  The 
Microscope  may  be  either  used  by  the  light  of  the 
sun  in  the  daytime,  or  at  night  by  some  form  of 
artificial  light.  It  is  best  used  by  daylight,  as 
artificial  light  is  likely  to  tire  the  eyes. 

Having  determined  to  work  by  daylight,  some 
spot  should  be  selected  near  a  window,  out  of  the 


28 


THE    STKUCTCRE    OF 


direct  light  of  the  sun,  in  which  to  place  a  small, 
firm,  steady  table.  On  this  the  Microscope  should 
be  placed,  and  the  object- 
1  glass  should  be  screwed  on 
to  the  tube.  The  mirror 
should  be  then  adjusted  so 
as  to  throw  a  bright  ray  of 
light  on  to  the  object-glass. 
The  eye-piece  having  been 
previously  placed  at  the  top 
of  the  tube,  the  Microscope 
is  now  ready  to  receive  a 
transparent  object.  If  the 
object  to  be  examined  is  an 
animalcule,  it  may  be  con- 
veyed to  the  animalcule-cage 
by  means  of  a  glass  tube, 
called  a  pipette  or  dipping- 
tube  (fig.  12),  which  should 
be  dipped  into  the  water 
where  the  object  is  con- 
tained, with  the  finger 
covered  over  the  upper  orifice, 
so  that  no  air  can  escape. 
By  taking  the  finger  off 
when  the  tube  is  in  the 
water,  the  fluid  will  rush 
into  the  tube,  and  with  it 
the  object  to  be  examined. 
The  finger  is  again  applied 
Fig.  12.  Dipping  Tubes,  to  the  top  of  the  tube,  an  1 
the  fluid  obtained  conveyed 

to  the  animalcule-cage.  Only  such  a  quantity  of 
the  water  should  be  allowed  to  fall  out  of  the 
tube  on  to  the  cage  as  will  enable  the  observer 
to  put  on  the  cover  of  the  cage  without  pressing 


THE    MICROSCOPE.  29 

the  fluid  out  at  the  sides  of  the  cage.  If  the 
water  is  thus  allowed  to  overflow,  it  runs  over 
the  glasses  of  the  cage,  and  thus  obscures  vision. 
An  object  or  objects  having  been  thus  placed 
in  the  cage,  it  is  conveyed  to  the  stage,  and 
placed  in  such  a  position  that  the  ray  of  light 
passing  from  the  mirror  to  the  object-glass  may 
pass  through  it.  This  having  been  done,  the 
observer  must  now  place  his  eye  over  the  eye-piece, 
and  use  the  screw  in  the  tube,  and  move  the  object- 
glass  downwards  until  he  gets  a  clear  view, of  objects 
moving  in  the  water.  This  is  called  focussing. 
The  glass  may  then  be  moved  up  or  down,  in 
order  that  the  best  view  of  the  object  may  be 
obtained.  When  the  object-glass  is  one  of  high 
power,  the  fine  adjustment  may  be  used  for  this 
purpose.  When  the  proper  focus  is  obtained,  the 
object  may  be  moved  up  or  down,  right  or  left, 
with  the  hand,  or  by  the  aid  of  the  screws  which 
are  employed  in  the  various  forms  of  what  are  called 
mechanical  stages. 

When  objects  not  requiring  the  live-box  or 
animalcule  -  cage  are  to  observed,  they  may  be 
transferred  to  the  glass  slide  by  aid  of  a  thin  slip 
of  wood,  or  a  porcupine-quill  moistened  at  the  end, 
or  by  a  pair  of  small  forceps.  (Fig.  8.)  Some 
transparent  objects  may  be  seen  without  any  me- 
dium, but  generally  it,  is  best  to  place  them  011  the 
slide  with  a  drop  or  two  of  clean  water,  which  may 
be  placed  on  it  with  a  dipping-tube.  When  water 
is  used,  it  will  generally  be  found  best  to  cover  the 
object  with  a  small  piece  of  thin  glass.  Small 
square  pieces  of  thin  glass  are  sold  at  all  the 
opticians'  shops  for  this  purpose.  The  object  is 
then  placed  under  the  object-glass  as  before. 

In  order  to  render  objects  transparent,  so  that 


30 


THE    STRUCTURE    OF 


they  may  be  viewed  by  transmitted  light,  very 
thin  sections  of  them  should  be  made.  This  may 
be  effected  by  means  of  a  very  sharp  scalpel,  or  a 
razor..  When  objects  are  too  small  to  be  held 
in  the  hand  to  be  cut,  they 
may  be  placed  between  two 
pieces  of  cork,  and  a  section  of 
them  made  at  the  same  time 
that  the  cork  is  cut  through. 

Sometimes  it  is  found  desir- 
able to  unravel  an  object  under 
the  Microscope.  If  this  is  the 
case,  only  a  low  power  should 
be  used,  and  the  object  may  be 
placed  on  a  glass  slide,  without 
any  glass  over,  and  two  needles 
with  small  wooden  *  handles 
employed, —  ordinary  sewing 
needles,  with  their  eyes  stuck 
in  the  handle  of  a  hair  pencil, 
will  answer  very  well.  (Fig.  14.) 
Even  when  dissection  is  not 
to  be  carried  on  under  the 
Microscope,  a  pair  of  needles 
of  this  sort,  for  tearing  minute 
structures  in  pieces,  will  be 
found  very  useful. 
*&• 14<  When  opaque  objects  are 

Dissecting  Needles.  to  ^e  examined,  the  light  from 
the  mirror  may  be  shut  off,  and  the  aid  of  the 
bull's-eye  condenser  called  in.  The  object  being 
secured  in  the  forceps  attached  to  the  stage 
(fig.  15),  or  laid  upon  a  slide,  the  light  is  allowed 
to  fall  on  it  through  the  condenser.  (Fig.  9.)  The 
object-glass  must  be  focussed  in  the  same  manner 
as  for  transparent  objects,  till  the  best  distance  is 


THE   MICROSCOPE. 

secured  for  examining  it.  The  petals  of  plants, 
the  wings  and  other  parts  of  insects,  with  many 
other  objects,  can  only  be  examined  in  this  way. 


Fig.  15.     Stage  Forceps. 

Even  the  beginner  will  find  it  useful  to  keep  by 
him  some  little  bottles,  containing  certain  chemical 
re-agents.  Thus,  a  solution  of  iodine  is  useful  to 
apply  to  the  tissues  of  plants,  for  the  purpose  of 
ascertaining  the  presence  of  starch.  This  solution 
may  be  made  by  adding  five  grains  of  iodine  and 
five  grains  of  iodide  of  potassium  to  an  ounce  of 
distilled  water.  It  turns  starch  blue  and  cellulose 
brown.  Cellulose  is  the  substance  that  forms  the 
walls  of  the  cells  in  plants.  Dilute  sulphuric  acid 
(1  to  3)  is  also  useful  as  a  re-agent ;  if  applied  to 
cellulose  previously  stained  with  iodine,  it  imparts 
a  blue  or  violet  tint.  Strong  nitric  acid  turns 
albuminous  matter  a  deep  yellow;  and  when 
diluted  (1  to  4)  with  water  is  used  for  separating 
the  elementary  tissues  of  vegetable  substances  either 
by  boiling  or  maceration. 

The  strong  solution  of  potash  (liquor  potassse) 
can  also  be  employed  with  advantage  in  softening 
and  making  clear  opaque  animal  and  vegetable 
substances.  While  using  these  powerful  agents, 
great  care  should  be  taken  to  prevent  the  trans- 
parency of  the  object-glass  becoming  impaired  by 
contact  with  them  or  by  long  exposure  to  their 
vapours. 


A    HALF    HOUR    WITH    THE 


CHAPTER    II. 

A  HALF-HOUR  WITH  THE  MICROSCOPE 
IN  THE  GARDEN. 

AMOXGST  the  objects  which  can  be  examined  by 
the  Microscope,  none  are  more  easily  obtained  than 
plants.  All  who  have  a  Microscope  may  not  be 
fortunate  enough  to  have  a  garden  ;  but  plants  are 
easily  obtained,  and  even  the  Londoner  has  access 
to  an  unbounded  store  in  Coven t  Garden.  We 
will,  then,  commence  our  microscopic  studies  with 
plants.  On  no  department  of  nature  has  the 
Microscope  thrown  more  light  than  on  the  struc- 
ture of  plants ;  and  we  will  endeavour  to  study 
these  in  such  a  manner  as  to  show  the  importance 
of  the  discoveries  that  have  been  made  by  the  aid 
of  this  instrument. 

If  we  take,  now,  a  portion  of  a  plant,  the  thin 
section  of  an  apple,  or  a  portion  of  the  coloured 
parts  of  a  flower,  or  a  section  of  a  leaf,  and  place 
it,  with  a  little  water,  on  a  glass  slide  under  the 
Microscope,  we  shall  see  that  these  parts  are  com- 
posed of  little  roundish  hollow  bodies,  sometimes 
pressed  closely  together,  and  sometimes  loose, 
assuming  very  various  shapes.  These  hollow 
bodies  are  called  "  cells,"  jand  we  shall  find  that  all 
parts  of  plants  are  built  tip  of  cells.  Sometimes, 
however,  they  have  so  far  lost  their  cellular  shape 
that  we  cannot  recognize  it  at  all.  Nevertheless, 
all  the  parts  we  see  are  formed  out  of  cells.  Cells 
tolerably  round,  and  not  pressed  on  each  other, 
may  be  seen  in  most  pulpy  fruits.  In  fact,  with 
a  little  care  in  making  a  thin  section,  and  placing 


PLATE 


°        XL 


TuffeaWest  sc  adnat. 


London.  Tbfcert  Sardmcte, 


MICROSCOPE   IN   THE   GARDEN.  33 

it  under  the  Microscope,  the  cellular  structure  of 
plants  may  be  observed  in  all  their  soft  parts. 

If,  now,  we  take  a  thin  section  from  an  apple,  or 
other  soft  fruit,  or  from  a  growing  bud,  or  tuberous 
root,  as  the  turnip,  we  shall  find  that  many  of  the 
cells  contain  in  their  interior  a  "  nucleus,"  or 
central  spot,  a  representation  of  which  is  seen 
from  the  cells  of  an  apple  in  figure  1  of  the  first 
plate.  This  nucleus  is  a*  point  of  great  import- 
ance in  the  history  of  the  cell,  for  it  has  been 
found  that  the  cell  originates  with  it,  and  that  all 
cells  are  either  formed  from  a  nucleus  of  this  kind, 
or  by  the  division  of  a  thin  membrane  in  the  inte- 
rior of  the  cell,  which  represents  the  nucleus,  and 
is  called  a  "  primordial  utricle." 

When  the  cells  of  plants  have  thus  originated, 
they  either  remain  free  or  only  slightly  adherent  to 
each  other,  or  they  press  upon  each  other,  assuming 
a  variety  of  shapes  ;  they  then  form  what  is  called 
a  "  tissue."  When  cells  are  equally  pressed  on  all 
sides,  they  form  twelve-sided  figures,  which,  when 
cut  through,  present  hexagonal  spaces.  This  may 
be  seen  in  the  pith  of  most  plants,  more  especially 
the  common  elder,  which  is  seen  at  figure  2  of 
plate  1.  Transverse  slices  of  the  stems  of  any 
kind  of  plant  from  the  garden  may  be  made  by  a 
razor,  or  sharp  penknife,  and  will  afford  interesting 
objects  for  the  Microscope. 

Cells,  during  their  growth,  assume  a  variety  of 
shapes,  and  the  tissues  which  they  form  are  named 
accordingly.  Two  examples  of  such  cells  will  be 
seen  in  figures  243  and  244  in  plate  8,  where  the 
first  represent  cells  from  the  hard  shell  of  a  plum 
stone,  and  the  second  the  thin  cells  from  the  out- 
side of  the  seed  of  the  guelder  rose.  'Sometimes  the 
cells  are  very  much  elongated,  or  they  unite  together 
to  form  an  elongated  tube  ;  the  tissue  thus  formed  is 


34  A    HALF    HOUR    AVITII    THE 

called  "  vascular  tissue  ;"  but  where  tlie  cells  retain 
their  primitive  form,  it  is  called  "  cellular  tissue."  A 
very  interesting  form  of  the  latter  is  the  "  stellate" 
tissue  found  in  most  water  plants,  and  especially 
regularly  developed  in  the  common  rush,  a  represen- 
tation of  which  is  given  in  figure  3  plate  1.  The 
object  of  this  tissue  is,  evidently,  to  allow  of  the 
existence  of  a  large  quantity  of  air  in  the  spaces 
between  the  cells  j  by  which  means  the  stem  of 
the  plant  is  lightened,  and  it  is  better  adapted  for 
growth  in  water. 

If  the  leaf  of  any  plant  is  examined,  it  will  be 
found  that  on  the  external  surface  there  is  a  thin 
layer,  called,  after  the  thin  external  membrane  in 
animals,  the  "  epidermis."  This  layer  is  composed 
of  very  minute  cells — smaller  than  those  in  other 
parts  of  the  plant,  and  when  placed  under  the 
Microscope,  presents  a  variety  of  forms  of  cellular 
tissue.  The  form  of  epidermal  cells  from  various 
plants  is  seen  in  figure  42  and  the  following 
figures  in  plate  2.  There  is  found  in  this  layer  a 
peculiar  organ  which  exists  on  the  outside  of  all 
parts  of  plants,  and  which  demands  attention.  In 
the  midst  of  the  tissue,  at  very  varying  distances, 
are  placed  little  openings,  having  a  semilunar  cell 
on  each  side.  These  openings  are  called  "  sto- 
mates,"  and  can  be  well  seen  in  the  leaf  of  the 
hyacinth,  which  is  shown  in  figure  42,  where  the 
cells  of  the  epidermis  are  transparent ;  but  the 
little  cells  which  form  the  stomate  are  filled  with 
green  colouring-matter.  The  stomates  vary  very 
much  in  size  and  in  numbers.  They  are  found  in 
larger  numbers  on  the  lower  than  on  the  upper 
side  of  leaves.  In  the  common  water-cress  they 
are  very  small,  as  seen  in  figure  43,  plate  2,  and 
the  cells  of  the  epidermis  are  sinuous.  The  sto- 
mates are  found  on  all  plants  having  an  epidermis. 


MICROSCOPE    IN    THE    GARDEN.  3g 

In  figures  44  and  46  they  are  represented  from 
the  wheat  and  the  aloe.  In  the  latter  plant  the 
cells  of  the  cuticle  are  very  much  thickened. 
They  can  also  be  seen  on  the  cuticle  of  the  fruit, 
as  shown  from  the  holly  in  figure  241,  plate  8, 
and  also  on  the  organs  and  petals.  These  form  a 
beautiful  object  under  the  Microscope.  The  petal 
of  the  common  scarlet  geranium  (Pelargonium) 
affords  a  beautiful  instance  of  the  way  in  which 
the  cells  of  plants  become  marked,  by  their  pecu- 
liar method  of  growth.  This  is  illustrated  in  the 
cells  of  the  common  red-flowered  geranium  at 
figure  45,  in  plate  2. 

The  vascular  tissue  of  plants  is  either  plain  or 
marked  in  its  interior.  If  we  examine  the  ribs  of 
leaves,  the  green  stems  of  plants,  or  a  longitudinal 
section  of  wood,  elongated  fibres,  lying  side  by  side, 
are  observed,  as  is  seen  in  the  case  of  the  elder,  at 
figure  53,  plate  2.  This  is  what  is  called  "lig- 
neous" or  "woody"  tissue,  and  the  greater  part 
of  the  wood  and  solid  parts  of  plants  are  com- 
posed of  this  tissue.  Such  tissue  is  seen  upon 
the  shoots  of  the  young  vine  in  figure  249, 
plate  8.  The  fibres  mostly  lie  in  bundles,  and  are 
divided  from  each  other  by  cellular  tissue.  This 
latter,  in  the  woody  stems  of  trees,  constitutes  the 
"medullary  rays,"  which  are  seen  in  transverse 
sections  of  stems,  extending  from  the  pith  to  the 
bark.  The  difference  observable  in  the  distribution 
of  the  woody  fibres  and  the  medullary  rays  renders 
the  examination  of  transverse  sections  of  the  stems 
of  plants  a  subject  of  much  interest ;  figure  54 
and  the  following  figures  in  plate  3,  present  the 
appearances  of  thin  sections  of  various  kinds  of 
wood  (figures  54,  55,  56,  57,  plate  3).  In  the 
transverse  sections  of  stems  of  most  plants,, 
large  open  tubes  are  observed.  This  is  seen  in 
D  2 


36  A    HALF-HOUR   WITH    THE 

the  case  of  the  oak,  figured  at  figure  55,  plate  3. 
These  are  called  "  ducts,"  Such  dacts  may  be  well 
observed  in  the  transverse  section  of  the  common 
radish,  as  seen  at  figure  51,  plate  2,  and  in  other 
roots.  These  ducts  are  often  marked  by  pores,  or 
dots,  and  are  hence  called  u  dotted  ducts."  These 
dots  are  the  result  of  deposits  in  the  interior  of 
the  tube  of  which  the  duct  is  formed,  and  a  great 
variety  of  such  markings  are  found  in  the  interior 
of  vascular  tissue.  One  of  the  most  common 
forms  of  marked  vascular  tissue  is  that  which  is 
called  glandular  woody  tissue,  of  which  a  figure  is 
given  at  54,  plate  3.  This  kind  of  tissue  is  found 
in  all  plants  belonging  to  the  cone-bearing,  or  fir 
tribe  of  plants.  In  order  to  discover  it,  recourse 
need  not  be  had  to  the  garden  for  growing  plants, 
as  every  piece  of  furniture  made  of  deal  wood  will 
afford  a  ready  means  of  obtaining  a  specimen.  All 
that  is  necessary  to  observe  the  little  round  disks 
with  a  black  dot  in  the  middle  is  to  make  a  thin 
longitudinal  section  of  a  piece  of  deal,  and  place  it 
under  a  half  or  quarter-inch  object-glass,  when 
they  will  be  readily  apparent.  The  application  of 
a  drop  of  water  on  the  slide,  or  immersing  them 
in  Canada  balsam,  will  bring  out  their  structure 
better. 

If  we  take  the  leaf-stalk  of  a  strawberry,  or  of 
garden  rhubarb,  and  make  a  transverse  section  all 
round,  nearly  to  the  centre  of  the  stalk,  the  lower 
part  will  at  last  break  off,  but  be  still  held  to  the 
upper  by  very  delicate  threads.  If  we  examine 
these  threads,  we  shall  find  that  they  are  fibres 
which  have  been  left  by  the  breaking  of  the  vessel 
in  which  they  were  contained  :  such  fibres  are  seen 
at  figure  48,  plate  2.  These  vessels  are  called 
"  spiral  vessels,"  and  are  found  in  the  stems  and 
leaves  of  many  plants.  They  are  seen  rolled  up  aa 


MICROSCOPE   IN   THE    GARDEN.  37 

found  in  the  garden  rhubarb,  at  figure  47,  plate  2. 
Sometimes  these  vessels  are  found  branched,  as  in 
the  common  chickweed,  which  is  seen  at  figure  50, 
plate  2.  This  arises  from  two  spires  coming  in 
contact  with  each  other,  and  adhering.  Occasion- 
ally the  spiral  fibre  breaks,  or  is  absorbed  at  certain 
points,  leaving  only  a  circular  portion  in  the  form 
of  a  ring,  as  seen  in  a  vessel  from  the  root  of 
wheat  at  figure  49,  plate  2.  Such  vessels  are 
called  "annular,"  and  may  be  observed  in  other 
roots  besides  those  of  growing  wheat,  as  in  the 
leaves  of  the  garden  rhubarb.  A  modification  of 
this  kind  of  tissue  is  seen  in  the  stems  and  roots 
of  ferns,  in  which  the  vessel  assumes  a  many-sided 
form.  This  kind  of  tissue  is  called  "  scalariform," 
or  ladder-like,  and  is  seen  in  figure  52,  plate  2. 
Sometimes  the  spiral  fibre  is  free.  This  is  repre- 
sented at  figure  250,  plate  8,  from  the  testa  of  the 
seed  of  the  wild  sage. 

The  bark  as  well  as  the  wood  of  trees  affords  the 
same  appearance  under  the  Microscope.  If  a  piece 
of  the  bark  of  any  plant  be  examined  by  means  of 
a  very  thin  transparent  section,  and  placed  upon  a 
slide,  and  put  under  an  inch  or  a  half-inch  object- 
glass,  the  structure  of  the  bark  may  be  easily  seen. 
On  the  outside  of  all  is  the  cuticle,  or  epidermis, 
and  under  this  lie  two  layers,  composed,  like  the 
cuticle,  of  cellular  tissue ;  but  the  inner  layer, 
before  we  come  to  the  wood  of  the  stem,  is  com- 
posed of  woody  tissue.  The  cellular  layer,  next  the 
woody  one,  is  often  developed  to  a  very  great  extent, 
and  then  constitutes  what  we  know  by  the  name  of 
cork.  The  bark  from  which  corks  are  made  is 
obtained  from  an  oak  tree  which  grows  in  the 
Levant.  If  we  make  a  very  thin  section  of  a  cork, 
its  cellular  structure  can  be  easily  made  out.  The 
cells  are  almost  cubical,  and  when  submitted  to  the 


A    HALF-HOUR   WITH   THE 

action  of  a  little  solution  of  caustic  potash,  they 
may  frequently  be  seen  to  be  slightly  pitted.  This 
is  represented  from  cork  in  figure  59,  plate  3. 

Many  of  the  structures  which  are  described  above 
may  be  seen  in  common  coal ;  thus  proving  most 
satisfactorily  that  this  substance  has  been  formed 
from  a  decayed  vegetation.  A  transverse  and  a 
longitudinal  section  of  coal  is  shown  at  figures  60 
and  61,  plate  3.  The  examination  of  coal,  how- 
ever, is  by  no  means  an  easy  task,  and  the  hands 
and  fingers  may  be  made  very  black,  and  the 
Microscope  very  dirty,  without  any  evident  struc- 
ture being  made  out.  Some  kinds  of  coal  are 
much  better  adapted  for  this  purpose  than  others. 
Sections  may  be  made  by  grinding,  or  coal  may  be 
submitted  to  the  action  of  nitric  acid  till  it  is 
sufficiently  soft  to  be  cut.  The  amateur  will  not 
find  it  easy  work  to  make  sections  of  coal ;  but 
should  he  wish  to  try,  he  may  fasten  a  piece  on  to 
a  slip  of  glass  with  Canada  balsam,  and  when  it 
has  become  firmly  fixed,  he  may  rub  it  down  on  a 
fine  stone  till  it  is  sufficiently  thin  to  allow  its 
structure  to  be  seen  under  the  Microscope.  Coal 
presents  both  vascular  and  cellular  tissue.  The 
vascular  tissue  is,  for  the  most  part,  of  the  glandular 
woody  kind ;  thus  leading  to  the  inference  that 
the  greater  portion  of  the  vegetation  that  supplied 
the  coal-beds  belonged  to  the  family  of  the  firs. 

The  external  forms  of  the  tissues  of  plants 
having  been  examined,  we  are  now  prepared  to 
regard  their  contents.  In  the  interior  of  the  cells 
forming  the  roots  and  the  growing  parts  of  plants 
will  be  observed  a  number  of  minute  grains, 
generally  of  a  roundish  form.  If  we  make  a  thin 
slice  of  a  potato,  these  granules  may  be  very  ob- 
viously seen,  lying  in  the  interior  of  the  cells  of 
which  the  potato  is  composed,  as  seen  at  figure  64, 


MICROSCOPE   IN    TI1E    GARDEN.  39 

plate  3.  If  we  now  take  a  drop  of  the  solution  of 
iodine,  and  apply  it  to  these  cells  full  of  granular 
contents,  we  shall  find  that  the  granules  assume  a 
deep-blue  colour.  This  is  the  proof  that  they  are 
starch  ;  and  as  far  as  we  at  present  know,  no  other 
substance  but  starch  has  the  power  of  assuming 
this  beautiful  blue  colour  under  the  influence  of 
iodine.  We  have  thus  a  ready  means  at  all  times 
of  distinguishing  starch.  The  grains  of  starch  are 
of  various  sizes  and  shapes.  The  starch  of  the 
flour  of  wheat  has  a  round  form,  and  varies  in  size  ; 
that  of  the  oat  is  characterized  by  the  small 
granules  of  starch  adhering  together  in  globular 
shapes.  When  these  globules  are  broken  up,  the 
grains  appear  very  irregular.  Grains  of  wheat 
starch  and  oat  starch  are  seen  in  figures  62  and  63, 
plate  3.  In  the  arrow-root  called  "  Tous  les 
Mois,"  the  grains  of  starch  are  the  largest  known, 
and,  like  those  of  the  potato,  they  look  as  if  com- 
posed of  a  series  of  plates  laid  one  upon  the  other, 
gradually  becoming  smaller  to  the  top.  This  is 
seen  at  figure  65,  plate  3.  These  lines  do  not, 
however,  indicate  a  series  of  plates,  but  appear 
more  like  a  series  of  contractions  of  a  hollow  vesicle 
or  bag.  This  vesicular  appearance  of  starch  may 
be  made  apparent  by  gently  heating  it,  after 
moistening,  over  a  spirit-lamp  on  a  glass  slide,  or 
by  dropping  on  it  a  drop  of  strong  sulphuric  acid. 
This  action  of  the  starch-granule  appears  to  be  duo 
to  the  fact  that  the  starch  is  converted  into  gum  by 
the  action  of  the  heat  on  the  sulphuric  acid.  Sago 
and  tapioca  are  almost  entirely  composed  of  starch, 
and  may  be  easily  examined  under  the  Microscope. 
Granules  of  sago  are  represented  in  figure  67,  and 
those  of  tapioca  at  figure  68 ;  they  are  readily 
distinguished  by  their  size.  The  starch  granules 
are  insoluble  in  water,  but  they  are  easily  diffused 


4-0  A   HALF -HOUR   WITH    THE 

through  it ;  so  that  by  washing  any  vegetable  tissue 
containing  starch,  with  water,  and  pouring  it  oft' 
and  allowing  it  to  stand,  the  starch  falls  to  the 
bottom.  This  may  be  done  by  bruising  the  vege- 
table tissue  in  a  mortar,  and  then  throwing  it  into 
cold  water.  The  tissue  falls  to  the  bottom,  and 
the  starch  is  thus  suspended  in  the  water.  In  this 
way  the  various  kinds  of  starches  may  be  procured 
for  microscopical  examination.  The  granules  of 
starch  have  frequently  a  little  black  irregular  spot 
in  their  centre.  In  the  starch  of  Indian  corn  it 
assumes  the  form  of  a  cross,  which  is  seen  at 
figure  66,  plate  3.  Starch  is  a  good  object  for 
the  use  of  the  polarizing  apparatus,  which  can  be 
applied  to  most  compound  Microscopes.  The 
grains  of  starch,  under  the  influence  of  polarized 
light,  become  coloured  in  a  beautiful  and  peculiar 
manner,  permitting  of  great  variation,  as  in  the 
case  of  all  polarized  objects. 

If  we  take  a  little  of  the  white  juice  from  the 
common  dandelion,  and  put  it  under  the  Micro- 
scope, we  shall  often  see,  besides  the  globules  of 
caoutchouc  which  make  the  juice  milky,  crystals 
of  various  forms.  Such  crystals  are  called  by  the 
botanist  "  raphides," — signifying  their  needle-like 
form.  They  arise  from  the  formation  and  accu- 
mulation of  insoluble  salts  in  the  fluids  of  the  plant. 
They  are  seen  in  various  plants,  and  under  very 
•different  circumstances.  Beautiful  needle-like  crys- 
tals can  be  seen  in  the  juice  of  the  common  hyacinth, 
represented  at  figure  69 ;  the  juice  may  be  ob- 
tained by  pressing.  A  question  has  been  raised  as 
to  whether  they  are  always  formed  in  the  cell.  They 
are  mostly  found  lying  in  the  cell,  as  in  the  leaves 
of  the  common  aloe,  seen  at  figure  70,  plate  3  : 
they  may  also  be  found  in  the  tissues  of  the  com- 
mon squill,  and  in  the  root  of  the  iris.  If  a  thin 


PLATE  '6. 


itj^ 


MICROSCOPE   IN   THE   GARDEN.  41 

nection  of  the  brown  outer  coat  of  the  common 
onion  is  made,  small  prismatic  crystals  are  observed. 
These  are  represented  at  figure  72,  plate  3.  Some- 
times several  of  these  crystals  unite  together  around 
a  central  mass,  forming  a  stellate  body.  These 
bodies  have  been  called  "  crystal  glands,"  but  they 
have  no  glandular  properties.  They  may  be  seen 
in  the  root  and  leaf-stalk  of  common  rhubarb,  and 
may  be  easily  observed  in  a  bit  of  rhubarb  from  a 
spring  tart.  From  such  a  source,  the  drawing  was 
made  at  figure  71.  These  crystals  are  mostly 
formed  of  oxalate  of  lime.  They  are  constantly 
found  in  plants  producing  oxalic  acid.  The  gritty 
nature  of  rhubarb  root  arises  from  the  presence  of 
oxalate  of  lime.  Sometimes  the  oxalate  of  lime 
assumes  a  round  dish-like  form.  Such  forms  are 
seen  in  plants  belonging  to  the  cactus  family.  A 
circular  crystalline  mass,  as  seen  in  a  common 
cactus,  is  represented  at  figure  73. 

Other  substances,  besides  oxalate  of  lime,  are 
found  crystallized  in  the  interior  and  on  the  surface 
of  plants.  Crystals  of  sulphate  of  lime  have  been 
found  in  the  interior  of  cycadaceous  plants.  Car- 
bonate of  lime  is  found  in  crystals  on  the  surface  of 
some  species  of  Chara,  or  stonewort.  There  is  a 
shrub  not  uncommon  in  gardens,  known  by  the 
name  of  Deutzia  scabra,  on  the  under  surface  of 
the  leaves  of  which  there  are  beautiful  stellate 
crystals  of  silica.  The  best  way  of  seeing  these  is 
to  put  the  leaf  under  the  Microscope,  and  to 
examine  it  by  the  aid  of  reflected  light. 

Sugar  and  honey  assume  a  crystalline  form,  and 
may  be  known  by  the  shape  of  their  crystals.  At 
figure  238,  plate  8,  a  crystal  of  honey  is  repre- 
sented ;  it  is  thinner  and  smaller  than  the  crystal 
of  cane  sugar  represented  at  figure  239.  Honey 
is  sometimes  adulterated  with  sugar.  Under  these 


42  A   HALF-HOUR   WITH    THE 

circumstances  the   sugar  crystal  loses  its  definite 
outline,  and  assumes  the  form  seen  at  figure  240. 

The  external  surface  of  the  parts  of  all  plants 
•will  afford  a  rich  field  of  amusement  and  instruc- 
tion to  the  microscopic  observer.  The  cuticle,  or 
epidermis,  of  which  we  have  before  spoken,  has  a 
very  varied  structure,  arid  contains  the  little  open- 
ings (stomates)  before  described.  The  cuticle,  which, 
in  a  large  number  of  cases,  is  smooth,  becomes 
elevated  in  some  instances,  and  forms  a  series  of 
projections,  which,  according  to  their  form,  are 
called  "  papillae,"  "  warts,"  "  hairs,"  "  glands,"  and 
"  prickles."  The  papillae  are  slight  elevations,  con- 
sisting of  one,  two,  or  more  cells ;  the  warts  are 
larger  and  harder;  whilst  the  hairs  are  long,  the 
glands  contain  a  secretion,  and  the  prickles  are 
hard  and  sharp.  For  examining  the  form  and 
growth  of  these  hairs,  the  flowers  of  the  common 
pansy  (heart's-ease)  afford  a  good  object.  Some  of 
the  projections  are  merely  papillae,  as  in  the  case 
of  the  kind  of  rudimentary  hair  represented  in 
figure  75,  plate  3 ;  others  are  found  longer,  and 
more  like  hairs,  as  seen  in  figure  76  j  whilst  others 
are  long,  and,  the  sides  of  the  hair  having  contracted, 
they  assume  the  appearance  of  a  knotted  stick,  as 
seen  in  the  hair  from  the  throat  of  the  flower  of  the 
pansy,  at  figure  78.  The  family  of  grasses,  wheat, 
barley,  oats,  and  other  forms,  are  favourable  sub- 
jects for  the  examination  of  simple  hairs,  or  hairs 
composed  of  a  single  elongated  cell.  At  figure  74, 
a  single  hair  is  given  from  a  common  grass.  All 
that  is  necessary  to  be  done,  in  order  to  see  these 
hairs,  is  to  take  any  part  of  the  plant  where  they 
are  present,  and  to  slice  off  a  small  portion  with  a 
sharp  penknife  or  razor,  and  place  it  under  the 
Microscope.  They  may  be  either  examined  dry,  or 
a  little  water  may  be  added,  and  a  piece  of  thin 


MICROSCOPE   IN   THE   GARDEN.  43 

glass  placed  over  them  on  the  slide.  Hairs  are 
frequently  formed  of  several  cells.  On  the  white 
dead-nettle  the  hairs  are  composed  of  two  cells,  as 
seen  in  figure  7  9 a.  The  nucleus,  or  cytoblast,  is 
often  seen  in  these,  and  is  represented  in  figures 
76,  77,  and  79,  plate  3.  On  the  common  groundsel 
hairs  may  be  seen,  composed  of  several  cells,  each 
cell  containing  a  nucleus,  as  at  figure  795.  Hairs 
like  a  string  of  beads  are  found  on  the  pimpernel 
and  sow-thistle,  which  last  will  be  found  in 
figure  80,  plate  3.  Occasionally  hairs  become 
branched.  Thus,  on  the  leaf  of  the  common 
chrysanthemum  the  hairs  present  the  form  of  the 
letter  T.  This  hair  is  represented  at  figure  82. 
On  the  under-surface  of  the  leaves  of  the  common 
hollyhock  hairs  are  seen  with  several  branches, 
giving  them  a  stellated  appearance,  as  seen  at 
figure  84.  The  common  lavender  is  covered  with 
stellate  hairs,  as  seen  at  figure  S5a.  These 
hairs  may  be  examined  as  opaque  or  transparent 
objects,  when  immersed  in  a  little  glycerine. 
The  hair  of  the  tobacco  plant  presents  a  peculiar 
knobbed  appearance.  The  presence  of  these  hairs 
is  a  test  of  the  purity  of  tobacco.  It  is  shown 
in  figure  81.  The  verbena  has  rosette -shaped 
hairs,  as  in  figure  83.  Sometimes  hairs  are 
covered  over  with  little  dots,  which  are  supposed 
to  be  deposited  after  the  growth  of  the  cells  of 
the  hair.  Such  hairs  may  be  seen  in  the  common 
verbena,  and  are  represented  at  figure  856. 
Hairs  are  sometimes  loose  and  long,  as  in  the 
white  poplar,  seen  at  figure  86.  Occasionally  an 
elevation,  consisting  of  several  cells,  is  formed  at 
the  base  of  a  hair.  These  are  shown  in  figure  87. 
When  these  cells  contain  a  poisonous  secretion, 
which  is  transmitted  along  the  tube  of  the  hair,  the 
hair  is  called  a  glandular  hair,  or  sting.  Such  are 


44  A   HALF-HOUR  WITH   THE 

the  hairs  of  the  common  stinging-nettle,  represented 
at  figure  SSa. 

The  hairs  constituting  the  down  or  "  pappus  "  of 
compositous  plants  assume  a  variety  of  forms.  The 
seed  or  fruit  of  the  common  groundsel  has  a  beau- 
tiful crown,  given  at  figure  245,  in  plate  8.  The 
pappus  of  the  dandelion  appears  notched,  as  seen 
at  figure  246.  The  burdock  has  a  cottony  hair, 
while  the  goatsbeard  is  like  a  feather, — both  of 
which  are  represented  respectively  in  figures  247 
and  248. 

If  a  hair  is  examined  in  its  growing  state,  with 
an  object-glass  of  one  quarter  of  an  inch  focus,  a 
movement  of  the  particles  in  its  interior  is  often 
observed.  This  is  easily  seen  in  the  hairs  around 
the  stamens  of  the  common  Spider  wort  (Trades- 
cantia  Virginica).  Such  movements  are  very  com- 
mon in  the  cells  of  water  plants.  One  of  those 
most  commonly  cultivated  in  aquavivaria  at  the 
present  day,  the  Valisneria  spiralis,  affords  the  best 
example  of  this  interesting  phenomenon.  In  order 
to  observe  this  movement,  a  growing  leaf  of  the 
valisneria  should  be  taken,  and  a  longitudinal  slice 
should  be  removed  from  its  surface,  by  means  of  a 
sharp  penknife  or  razor.  The  slice,  or  the  sliced 
part  left  on  the  leaf,  should  now  be  put  on  a  slide, 
a  drop  or  two  of  water  added,  and  covered  with  a 
thin  piece  of  glass,  when,  after  a  little  time,  espe- 
cially in  a  warm  room,  the  movement  will  be  ob- 
served. This  movement  takes  place  in  the  little 
particles  around  the  sides  of  the  cells  represented 
in  figure  886,  plate  3.  It  may  also  be  seen  in 
the  leaves  of  the  new  water- weed  (Anacharis 
alsinastrum),  the  frogbit,  the  rootlets  of  wheat,  in 
the  family  of  charas,  and  in  the  cells  of  many  other 
water  plants.  In  examining  some  species  of  Chara, 
the  external  bark,  or  rind,  should  be  removed  from 


MICHOSCOPE   IX   THE   GARDEN.  45 

the  cells,  or  the  movements  will  not  be  seen.  This 
movement  seems  dependent  on  the  internal  proto- 
plasmic matter,  or  "  primordial  utricle,"  which  is 
contained  in  many  cells,  and  which,  in  these  cases, 
is  spread  over  the  interior  of  the  cell.  It  is,  how- 
ever, capable  of  contraction,  and  when  the  plants 
are  exposed  to  cold,  the  utricles  contract  and  pre- 
vent the  movement  of  the  contents  in  the  interior. 
It  is,  apparently,  the  extension  of  this  substance 
beyond  the  walls  of  the  cell  which  constitutes  the 
little  hairlike  organs  called  "  cilia,"  which  are  con- 
stantly moving,  and  by  the  aid  of  which  the  spores 
of  some  plants  effect  rapid  movements.  Such 
organs  are  found  in  the  Pandorina  Morum  and 
Volvox  globator,  moveable  plants  represented  at 
figures  13  and  14,  plate  1.  The  effect  of  these 
cilia  in  producing  the  movements  of  plants  is  well 
seen  in  the  Volvox  globator,  which,  on  account  of 
its  rapid  movements,  was  at  one  time  regarded  as 
an  animalcule,  but  it  is  now  regarded  as  a  plant. 
Cilia  are,  however,  more  frequently  met  with  in  the 
animal  kingdom.  They  are  seen  in  the  drawing  of 
Plumatella  repens,  at  a,  in  figure  163  of  plate  6. 

Amongst  the  parts  of  plants  which  can  alone 
be  investigated  by  the  Microscope  are  the  stamens. 
These  organs  are  situated  in  the  flower,  between 
the  petals  and  the  pistil,  and  usually  consist  of  a 
filament,  or  stalk,  with  a  knob  or  anther  at  its  top. 
If  the  anther  is  examined,  it  will  usually  be  found 
to  consist  of  two  separate  valves,  or  cases,  in  each 
of  which  is  contained  a  quantity  of  powder,  or  dust, 
called  "  pollen."  The  walls  of  these  valves  are 
worth  careful  examination  under  the  Microscope, 
on  account  of  the  beautifully-marked  cellular  tissue 
of  which  their  inner  walls  consist.  The  cells  of  this 
tissue  contain  in  their  interior  spiral  fibres  similar 
to  those  which  have  been  described  as  present  in 


46  A    HALF    HOUR   WITH    THE 

certain  forms  of  vascular  tissue.  In  the  anthers  of 
the  common  furze  the  fibres  are  well  marked,  and 
are  represented  in  figure  118,  plate  5  ;  in  the 
common  hyacinth  they  are  larger,  and  frequently 
present,  in  their  intercellular  spaces,  bundles  of 
raphides,  as  seen  at  Figure  119.  In  the  white 
dead-nettle  the  fibre  is  irregularly  deposited,  as  at 
figure  120.  In  the  anthers  of  the  narcissus,  given 
at  figure  121,  the  cells  are  almost  vascular  in  their 
structure,  and  present  the  same  appearance  as 
those  described  under  the  head  of  annular  ducts. 
The  reader  should  compare  figure  121,  plate  5, 
with  figure  49,  plate  2.  In  the  crown  imperial 
the  fibres  of  the  cells  radiate  from  a  central  point 
in  a  stellate  manner,  as  at  figure  122. 

When  the  anther-cases  have  been  examined,  a 
little  of  the  dust  may  be  shaken  on  to  a  slide,  and 
examined  as  an  opaque  or  a  transparent  object. 
Each  species  of  plant  produces  its  own  peculiar 
form  of  pollen.  These  little  grains  are  actual  cells. 
They  are  the  cells  of  plants  which  in  their  position 
in  the  anther  will  not  grow  any  further.  They  are 
destined  to  be  carried  into  the  pistil,  where,  meet- 
ing with  other  cells,  they  furnish  a  stimulus  to  their 
growth,  and  the  embryo,  or  young  plant,  is  pro- 
duced. The  history  cf  the  development  of  these 
cells,  as  well  as  of  those  in  the  interior  of  the  pistil, 
is  a  very  interesting  one,  and  is  one  of  those  sub- 
jects of  investigation  which  has  been  created  by 
the  aid  of  the  Microscope.  The  pollen  grains  vary 
in  size  as  well  as  form.  They  are  frequently  oval, 
as  seen  in  figure  123,  plate  5.  In  the  hazel  and 
many  of  the  grasses  they  are  triangular.  Those 
from  the  hazel  are  represented  at  figure  124.  In 
the  heath  they  are  tri-lobed,  as  at  figure  125  ;  in 
the  dandelion,  and  many  of  the  compositous  order 
of  plants,  they  are  beautifully  sculptured,  as  seen 


MICROSCOPE   IN    THE   GARDEN.  47 

at  figure  126.  IB  the  passion-flower,  three  rings 
are  observed  upon  them,  as  though  they  had  been 
formed  with  a  turner's  lathe — figured  at  127.  In 
the  common  mallow,  they  are  covered  all  over  with 
little  sharp-pointed  projections,  like  a  hand-grenade. 
These  are  represented  at  figure  128.  The  micro- 
scopic observer  should  make  himself  acquainted 
with  the  forms  of  pollen  grains,  as,  on  account  of 
their  small  size  and  lightness,  they  are  blown  about 
in  all  directions,  and  may  be  found  on  very  dif- 
ferent objects  from  those  in  which  they  have  been 
produced.  Some  absurd  mistakes  have  been  com- 
mitted by  confounding  pollen  grains  with  other 
forms  of  organic  matter.  Thus,  pollen  grains  in 
bread  were  regarded  as  bodies  connected  with  the 
production  of  cholera. 

The  pistil,  which  is  the  central  organ  seated  in 
the  midst- of  the  stamens  in  the  flower  of  plants, 
will  afford  a  great  variety  of  interesting  points  for 
examination  with  the  Microscope.  In  the  earliest 
stages  of  the  growth  of  the  pistil,  thin  sections  of 
it  may  be  made,  and  the  position  of  the  ovules 
observed.  In  the  ovule  will  be  found  the  embryo 
sac,  a  central  cell,  which,  on  being  brought  in 
contact  with  the  pollen  grain,  grows  into  the  seed. 
The  seed  contains  the  embryo,  or  young  plant.  In 
most  plants  this  is  sufficiently  large  to  be  seen 
by  the  naked  eye  ;  but  it  may,  nevertheless,  be 
examined  with  advantage  by  a  low  microscopic 
power  The  seed  is  covered  on  the  outside  with 
a  membrane,  which  is  called  the  "  testa."  This 
membrane  is  often  curiously  marked,  and  the  whole 
seed  may  be  examined  as  an  opaque  object  with 
the  low  powers  of  the  Microscope.  In  order  to  do 
this,  the  light  must  be  shut  oft"  from  the  mirror, 
and,  the  object  being  placed  on  the  stage,  a  pencil 
of  light  should  be  thrown  upon  it  by  the  aid  of  the 


43  A  nALF-nora  WITH  TEE 

bull's-eye  condenser.  If  a  seed  of  the  red  poppy 
be  now  examined,  it  will  be  found  to  have  a 
uniform  shape,  and  to  be  reticulated  on  its  surface, 
as  seen  at  figure  129,  plate  5.  The  seed  of  the 
black  mustard  exhibits  a  surface  apparently  covered 
with  a  delicate  network,  seen  at  figure  130.  Some 
seeds  have  deep  and  curved  furrows  on  their  sur- 
faces, such  as  exhibited  in  figure  131.  The  great 
snapdragon  has  a  seed  covered  with  irregular 
projecting  ridges,  having  a  granuled  appearance, 
represented  at  figure  132.  The  seed  of  the  chick- 
weed  presents  a  series  of  blunt  projections,  as  in 
figure  133.  In  the  various  forms  of  umbel- 
bearing  plants,  the  seeds  adhere  to  the  fruit,  and 
the  fruit  is  commonly  called  the  "  seed."  Such 
are  caraway,  coriander,  dill,  and  anise  seeds.  The 
plants  of  this  family  are  very  common  weeds  in 
our  gardens  and  fields,  and  may  be  easily  procured 
for  microscopic  examination.  Some  of  these  fruits 
are  covered  over  with  little  hooks,  seen  at  figure 
134,  whilst  others  present  variously -formed  ridges 
and  furrows,  which  are  amongst  the  best  means 
for  distinguishing  these  plants  the  one  from  the 
other. 


PhAIE   4 


London   Robert 


MICROSCOPE   IN   THE   COUNTRY.  49 


CHAPTER      III. 

A  HALF-HOUR  WITH  THE  MICROSCOPE 
IN  THE  COUNTRY. 

A  COMPOUND  Microscope  is  not  easily  conveyed  and 
put  up  in  the  fields,  but  the  produce  of  the  roads 
and  waysides  may  be  easily  brought  to  the  Micro- 
scope at  home.  No  one  who  has  a  Microscope 
should  walk  out  into  the  country  without  supply- 
ing himself  with  a  few  small  boxes,  a  hand- net, 
and  three  or  four  small  bottles,  in  order  to  bring 
home  objects  for  examination.  The  dry  produce, 
which  may  be  put  into  boxes,  is  of  a  different 
character  from  that  which  may  be  conveyed  home 
in  bottles.  We  shall,  therefore,  first  direct  attention 
to  the  minute  forms  of  mosses,  fungi,  lichens,  and 
ferns,  which  may  be  collected  in  boxes  ;  premising, 
however,  that  many  members  of  these  families  may 
be  found  without  going  into  the  country  to  seek  for 
them.  The  cheese  in  the  pantry,  and  the  decayed 
parts  of  fruits,  and  objects  covered  with  mould,  are 
good  subjects  for  microscopic  examination. 

Amongst  the  minuter  plants  and  animals  whose 
true  nature  can  only  be  detected  by  the  Microscope 
many  are  composed  of  a  single  cell,  whilst  others, 
like  higher  plants  and  animals,  are  formed  by  the 
union  of  a  large  number  of  cells.  The  greater 
proportion  of  the  one -celled,  or  unicellular  plants, 
as  they  are  called,  are  found  in  water  :  but  some 
are  found  on  moist  rocks,  stones,  and  old  walls. 
Amongst  these  there  is  one  of  exceedingly  simple 
structure,  called  gory  dew  (Palmdla  cruenta).  This 


•50  A  HALF-HOUB    WITII    THE 

plant  appears  as  a  red  stain  upon  the  surface  of 
damp  objects.  If  a  little  of  this  red  matter  is 
scraped  off  the  object  to  which  it  is  attached,  and 
placed  under  the  Microscope,  it  will  be  found  to 
consist  of  a  number  of  separate  minute  cells,  as 
represented  at  figure  89,  plate  4.  This  plant 
belongs  to  the  same  family  as  the  red-snow  plant, 
ard  there  are  a  number  of  forms  of  these  minute 
organisms,  which,  on  account  of  their  rapid  growth 
and  red  colour,  have  given  rise  to  alarming  appre- 
hensions, in  former  times,  when  their  true  nature 
was  imperfectly  understood.  One  of  them  attacks 
bread,  and  gives  to  it  the  appearance  of  having 
been  dipped  in  blood.  They  also  attack  potatoes. 
Of  the  same  simple  structure,  but  not  having  a  red 
colour,  is  the  yeast-plant,  or  fungus,  shown  at 
figure  90,  plate  4.  This  plant  abounds  in  yeast, 
and  may  also  be  found  in  porter  and  ale.  If 
vinegar  is  allowed  to  stand  for  some  time,  a 
minute  plant  is  developed,  called  the  vinegar- 
plant.  In  its  earlier  stages  of  growth  it  exhibits 
elongated  cells,  looking  like  broken  pieces  of 
thread,  seen  at  figure  91.  Threads  more  fully 
developed  are  often  seen  in  decomposing  fluids, 
and  upon  the  surface  of  decomposing  animal  and 
vegetable  substances ;  such  is  the  so-called  cholera- 
fungus,  which  may  be  obtained  by  exposing  damp 
slides  to  the  air.  They  are  shown  at  figure  92. 
Such  plant-like  threads  can  be  collected  from  the 
air  in  clamp  and  unwholesome  cellars  and  rooms, 
and  were  at  one  time  supposed  to  be  connected 
with  the  production  of  that  fearful  disease,  the 
cholera.  It  has  been  rendered,  however,  exceed- 
ingly probable  that  all  these  appearances  are  but 
different  forms  of  the  fungus  which  produces 
common  mould,  and  which  is  known  by  the  name 
of  Penicillium  glaucum.  This  fungus  is  represented 


MICROSCOPE   IN   THE    COUNTRY.  51 

at  figure  95.  It  may  be  found  on  the  surface  of 
preserves  and  jellies,  and  consists  of  a  mass  of  fila- 
ments or  threads  serving  as  its  base,  from  the 
surface  of  which  individual  filaments  rise  up,  bear- 
ing a  number  of  minute  cells,  which  are  the 
spores,  or  reproductive  organs.  These  are  seen  at 
figure  96. 

Plants  such  as  these,  and  belonging  to  the  family 
of  fungi,  are  found  everywhere  on  the  leaves  of 
plants  in  the  summer  and  autumn,  forming  irre- 
gular spots,  of  a  yellow,  red,  or  black  colour.  If 
such  leaves  are  brought  home  and  placed  under  the 
Microscope,  they  present  a  never-failing  source  of 
interest.  The  red  appearance  on  the  leaves  of 
wheat,  called  the  rust,  is  due  to  one  of  these  fungi, 
seen  at  figure  93,  plate  4.  This  appears  to  be  an 
early  stage  of  the  fungus,  which  produces  what  is 
called  mildew,  and  is  represented  at  figure  94. 
These  fungi  are  so  common  on  the  wheat-plant 
that  their  spores  mingle  with  the  seeds  when 
ground  into  flour,  and  can  be  found,  when  care- 
fully sought  for,  in  almost  every  piece  of  bread 
that  is  examined  under  the  Microscope.  Mouldy 
grapes,  pears,  apples,  and  other  fruits,  present  fungi, 
having  the  same  general  form  as  that  of  common 
mould.  Such  a  fungus  is  the  Botrytis  of  mouldy 
grapes  seen  at  figure  96.  Mouldy  bread  also  pre- 
sents a  fungus  of  this  kind.  This  species  is  called 
Mucor  mucedo,  and  is  represented  at  figure  97.  Its 
spores  are  arranged  in  a  globular  form.  A  fungus 
not  unlike  the  last  has  been  described  as  growing 
in  the  human  ear,  and  is  figured  at  98.  The 
leaves  of  the  common  bramble  present  a  fungus 
in  which  the  spores  are  arranged  on  a  more  dense 
and  elongated  head.  This  is  called  Phragmidium 
bulbosum,  and  is  represented  at  figure  99.  The 
Outturn  which  attends  the  blight  of  the  vine,  seen 
E  2 


52  A  HALF-HOUR    WITH    THE 

at  figure  100,  and  the  Botrytis  which  accompanies 
the  potato  disease,  figure  101,  are  other  and  in- 
teresting forms  of  these  minute  parasites.  The 
common  pea  is  subject  to  a  blight  which  is  ac- 
companied by  a  peculiar  fungus,  seen  at  figure  102a, 
which,  when  examined  by  a  low  power,  presents  a 
globular  mass,  surrounded  by  minute  filaments. 
Under  a  high  power  the  central  ball  is  resolved 
into  a  series  of  little  cases,  containing  in  their 
interior  the  minute  spores.  These  are  seen  at 
figure  1026.  Seeds,  as  well  as  fruits,  are  liable  to 
the  attacks  of  fungi  during  their  decay.  Figure  103. 
Plate  4,  represents  a  fungus  found  in  a  mould  upon 
a  common  Spanish  nut.  This  fungus  looks  like  a 
red  powder  spread  over  the  surface  of  the  nut.  A 
fungus  has  been  described  as  attacking  the  oil- 
casks  in  the  London  docks :  its  fibres  resemble 
threads  of  black  silk.  It  is  represented  at 
figure  104.  The  spores  are  found  scattered  about 
the  fibres.  As  we  have  already  seen,  fungi  are 
found  on  the  human  body,  and  accompany  certain 
forms  of  disease  of  the  skin,  more  especially  those 
of  the  head.  In  these  cases  the  fungi  insert  them- 
selves into  the  follicle  of  the  hair,  and  introduce 
themselves  into  its  structure,  so  that  it  either  falls 
off  or  becomes  disorganized.  The  fungus  of  ring- 
worm, called  Achorion  Schonlenii,  is  given  at 
figuie  105.  If  the  seed  of  wheat  is  allowed  to 
germinate  in  a  damp  place,  the  little  rootlet  which 
it  sends  down  will  be  found  covered  over  with  a 
minute  fungus.  A  fungus  of  some  interest,  on 
account  of  its  unusual  place  of  growth,  may 
be  found,  in  autumn,  attached  to  the  roots  of 
the  common  duck-weed  (Lemna  minor),  seen  at 
figure  106  —  plate  4.  In  the  same  figure,  at «, 
is  represented  a  fungus  of  a  different  kind,  it  is 
parasitic  within  the  cells,  and  has  a  bead-liko 


MICROSCOPE   IN   THE   COUNTRY.  53 

appearance.      It  may  be  an  earlier  stage  of  the 
growth  of  the  former. 

The  microscopic  structure  of  the  higher  forms  of 
fungi  is  not  without  its  interest.  In  the  fungi  a 
very  elongated  form  of  cellular  tissue  frequently 
occurs,  and  in  the  stem  of  the  common  mushroom 
it  will  be  seen  to  be  branched,  as  at  figure  103. 
The  looser  portions  of  the  fibres  of  the  mushroom, 
which  are  found  in  the  earth  at  the  bottom  of  the 
stem,  afford  even  a  better  illustration  of  this  struc- 
ture, and  is  given  at  figure  107.  The  gills  of  the 
mushroom,  when  put  under  the  Microscope,  display 
a  number  of  small  projections  surmounted  with 
four  round  cells ;  these  are  the  spores  arranged  in 
fours,  and  which,  on  that  account,  are  called  tetra- 
S2)ores.  They  are  seen  at  c,  figure  107. 

In  the  woods,  in  winter  time,  fungi  abound,  and 
their  parts  may  be  examined  under  the  Microscope 
with  great  interest.  Amongst  the  winter  beauties 
of  the  forest,  none  are  more  attractive  than  the 
various  forms  of  peziza,  or  cup-moulds.  If  a  section 
be  made  through  one  of  the  cups  of  these  beautiful 
fungi,  they  will  present  the  appearance  drawn  in 
figure  108,  plate  4.  A  series  of  hollow  elongated 
cases  will  be  found  lying  between  compressed  elon- 
gated tissue.  In  these  cases  a  series  of  rather  oval 
minute  cells  will  be  found,  which  are  the  spores  of 
the  peziza.  If  these  are  magnified  with  a  higher 
power,  they  will  be  seen  to  be  covered  over  with 
minute  spines,  as  seen  at  a. 

Amongst  the  objects  which  more  especially 
attract  the  attention  of  observers  in  the  country, 
in  winter  time,  are  the  various  forms  of  lichens, 
which  grow  parasitic  upon  the  bark  of  trees.  There 
is  one  of  a  yellow  colour,  which  spreads  on  palings 
and  the  barks  of  trees,  like  dried  pieces  of  yellow- 
paper.  At  the  surface  of  the  membranous  scales  of 


54  A  HALF-HOUR   WITH    THE 

which  the  plant  is  composed  will  be  found  deeper 
yellow  spots.  If  one  of  these  is  cut  through,  and  a 
thin  section  placed  under  the  Microscope,  it  will  be 
found  to  possess  very  similar  organs  to  the  peziza. 
A  series  of  cases  will  be  found,  containing  the 
minute  spores  by  means  of  which  the  plant  is 
reproduced.  These  cases,  called  asci,  are  figured 
at.  109. 

A  walk  across  a  damp  uncultivated  piece  of  ground 
will  not  fail  to  reveal  some  spots  which  are  boggy, 
Here  the  bog-moss  (Sphagnum}  must  be  looked  for, 
and  when  found,  it  may  be  regarded  as  a  good 
illustration  of  the  family  of  mosses,  and  portions 
preserved  for  microscopic  examination.  The  leaves 
afford  interesting  examples  of  fibro-cellular  tissue, 
as  seen  at  figure  110;  and  this  tissue  may  be 
examined  from  day  to  day,  as  affording  an  illus- 
tration of  the  process  of  development  in  vegetable 
tissue.  Other  forms  of  mosses  may  be  found  on 
banks,  old  walls,  rocks,  and  crevices.  The  organs 
which  produce  the  spores,  or  seeds,  are  well  de- 
serving the  attention  of  the  microscopic  observer. 
These  represent  the  pistils  in  the  higher  plants. 
The  organs  which  represent  the  stamens  are  also 
very  interesting,  but  they  are  not  so  easily  pro- 
cured. We  therefore  proceed  to  describe  the 
spore-bearing  organ.  This  may  be  easily  seen  with 
the  naked  eye,  although  its  beauties  cannot  be 
brought  fully  out  without  the  aid  of  the  Micro- 
scope. The  part  which  contains  the  spores  is 
seated  on  a  little  stalk,  and  is  called  the  "  urn," 
and  is  represented  in  figure  112.  Covering  the 
urn,  and  fitting  on  to  it  like  a  nightcap,  is  the 
calyptra,  marked  a.  On  slipping  off  the  calyptra, 
a  conical  body  fitting  into  the  urn  is  observed,  and 
this  is  called  the  "operculum"  (b).  If  the  operculum 
is  now  lifted  offt  there  is  revealed,  below,  a  series  of 


MICROSCOPE    IN   THE    COUNTRY. 

twisted  hair-like  threads  (c),  which  are  called  the 
"  peristome."  These  processes  are  held  together  by 
minute  teeth  (d).  The  spores  (e)  are  found  in  the 
interior  of  the  urn.  All  these  parts  are  subject  to 
great  varieties  in  different  kinds  of  mosses. 

.From  the  mosses  we  may  pass  on  to  the  feins. 
Like  the  mosses,  they  have  no  regular  flowers,  and 
the  parts  which  correspond  to  the  urns  of  the 
mosses  are  the  small  brown  scaly-looking  bodies 
seated  on  the  back  of  the  fronds,  or  leaves.  In  the 
male  fern  the  little  brown  bodies  which  contain 
the  spores  are  round,  as  seen  in  figure  113,  and  in 
the  common  brakes  they  are  placed  on  the  edge  of 
the  fronds,  as  at  figure  114.  These  organs,  which 
are  called  "  sori,"  may  be  easily  seen  as  opaque 
objects,  under  the  lower  powers  of  the  Microscope. 
In  the  common  hart's-tongue,  or  scolopendrium, 
the  sori  are  arranged  in  elongated  bands.  In  this 
case  the  sori  are  covered  with  a  membrane  called 
an  "  indusium."  On  opening  this,  the  sori  are 
found  lying  close  together.  Each  one  of  these  sori 
is  found  to  be  made  up  of  a  number  of  cases  called 
capsules,  or  "  thecae,"  attached  to  a  stalk  by  which 
they  are  fixed  to  the  frond.  This  organ  is  seen  at 
figure  115.  These  thecse  are  beautiful  objects 
under  the  Microscope.  Springing  from  the  top  of 
the  stalk  is  a  series  of  cells  which  surround  the 
case,  forming  what  is  called  the  rt  annulus."  This 
ring  possesses  an  elastic  power ;  so  that  when  it 
breaks,  the  capsule  is  torn  open,  and  the  spores 
in  the  inside  escape.  The  spores  are  covered  over 
with  little  spines,  as  at  a,  in  the  same  figure.  The 
spores  of  ferns  are  often  called  seeds,  but  they  are 
more  like  buds  than  seeds.  If  one  of  these  spores 
is  watched  during  its  growth,  it  will  be  found  that 
it  grows  into  a  little  green  membranous  expansion, 
on  the  surface  of  which  the  two  sets  of  organs 


56  A  HALF-HOUR    WITH    THE 

resembling  the  pollen  grains  and  ovules  of  the 
higher  plants  are  developed.  The  representatives 
of  the  pollen  grains  are  little  moving  bodies,  re- 
sembling animalcules,  which  pass  over  the  surface 
of  the  membranous  expansion  till  they  reach  the 
ovules,  or  true  spores  of  the  fern,  which  they  fer- 
tilize, and  the  young  plant  then  shoots  forth.  The 
ferns,  of  which  so  many  species  may  be  found  in  a 
walk  in  the  country,  or  cultivated  in  a  Ward's 
case  in  town,  are  worthy  the  minute  attention  of 
the  possessor  of  a  Microscope,  on  account  of  the 
great  variety  of  forms  which  their  organs  of  fructi- 
fication present. 

The  club-mosses  are  found  on  boggy  moors  and 
open  places,  and  present  a  variety  in  the  forms  of 
their  fructification.  The  reproductive  organs  are 
formed  out  of  a  transformed  branch,  and  are  found 
lying  at  the  base  of  scale-like  bodies,  resembling 
the  scales  which  form  the  fruit  of  firs  and  pine- 
trees,  as  seen  at  figure  115,  a.  The  spores  of  the 
club-mosses  are  of  two  kinds,  large  and  small ; 
hence  they  are  called  "  megaspores  "  and  "  micro- 
spores."  The  last  are  very  minute,  and  when 
highly  magnified,  they  present  a  reticulated  ap- 
pearance. The  spores  are  seen  at  b  and  c  in 
figure  117.  In  the  interior  of  these  spores  is  a 
minute  worm-like  body,  which  acts  the  part  of  the 
pollen  in  higher  plants.  The  megaspores  are  much 
larger.  They  represent  the  spores  of  ferns,  and 
produce  an  expanded  membrane,  on  which  grow 
the  true  representatives  of  the  ovules,  which 
coming  in  contact  with  the  microspores,  new  plants 
are  produced. 

Another  family  of  these  flowerless  plants,  which 
has  yielded  highly  interesting  results  to  the  micro- 
scopic observer  is  the  group  of  horsetails.  If  these 
are  gathered  in  the  spring  of  the  year,  they  will 


I 


London :  Hbbert  Ha.rcJmcke,1860/, 


MICROSCOPE    IN    THE   COUNTRY.  57 

present  two  forms ;  one  showing  the  leaves  and 
green  parts  of  the  fruit ;  the  other,  the  leaves 
changed  into  reproductive  organs.  These  may  be 
very  easily  examined  as  opaque  objects  under  the 
Microscope.  The  spores  are  seated  on  round  shield- 
like  disks,  represented  in  plate  4,  at  figure  116,  a. 
When  the  spores  are  examined  by  a  higher  power, 
they  present  four  spiral  filaments,  which  are  twisted 
round  the  body  of  the  spore,  and  seen  at  b.  If  the 
spore  is  breathed  upon  whilst  under  the  Microscope, 
the  spiral  filaments  gradually  relax  their  grasp,  and 
they  become  expanded  and  attached  to  the  spore 
only  at  one  end,  as  represented  at  c.  The  cuticles 
of  the  Equisetums  are  strongly  siliceous,  and  are 
very  curious  and  interesting  objects,  and  will  repay 
the  trouble  taken  in  preparing  them.  This  may 
be  done  by  boiling  a  piece  of  the  stem,  in  nitric 
acid  and  chlorate  of  potash,  and,  after  washing  the 
detached  cuticle,  transferring  it  to  absolute  alcohol, 
from  thence  to  oil  of  cloves,  and  afterwards 
mounting  in  Canada  balsam. 

The  study  of  the  flowerless  plants  is  one  of 
never-ceasing  interest.  Within  the  last  few  yeare 
much  has  been  done  by  the  aid  of  the  Microscope 
to  clear  away  the  mystery  which  surrounded  the 
functions  performed  by  certain  organs  they  possess. 
Much  more,  however,  remains  to  be  done ;  and  an 
interesting  field  is  still  open  to  the  inquiries  of  the 
microscopist.  We  will  now,  however,  take  our 
Microscope  to  the  pond-side,  where  we  shall  still 
find  many  plants  to  interest  us,  belonging  to  the 
lower,  or  flowerless  groups  together  with  animals, 
the  companions  of  their  aqaatic  life,  and  the  repre- 
sentatives of  their  simpler  mode  of  existence. 


58  A  HALF-HOUR  WITH    THE 


CHAPTER    IT. 

A  HALF-HOUR  WITH  THE  MICROSCOPE 
AT  THE  POND-SIDE. 

CISTERNS,  ditches,  ponds,  and  rivers,  contain  nume- 
rous objects  to  interest  the  microscopic  observer. 
Some  of  these  objects  float  on  the  surface  of  the 
water  ;  others  are  found  swimming  about  in  the 
midst  of  the  water ;  whilst  the  greater  number 
are  found  at  the  bottom.  In  collecting  objects 
from  fresh  water,  little  bottles  may  be  used,  and  a 
common  spoon  or  small  net  employed  for  collecting 
them.  Where  the  objects  are  only  few,  large 
quantities  of  the  water  should  be  allowed  to  stand, 
and  the  whole  poured  off,  with  the  exception  of  a 
table-spoonful  or  two,  which  may  be  then  placed 
in  a  wine-glass.  A  little  of  the  sediment  may  be 
taken  up  in  a  pipette  or  clipping-tube,  and  con- 
veyed to  the  animalcule-cage,  and  the  cover  having 
been  put  on,  it  may  be  placed  under  the  Micro- 
scope. If  the  objects  are  moving  about  too  rapidly, 
the  cover  may  be  pressed  down  till  they  are  secured. 
They  may  be  first  sought  out  with  a  low  power, 
and  when  it  is  wished  to  examine  them  more 
closely,  a  higher  power  may  be  put  on. 

Of  all  the  forms  of  microscopic  plants  which 
are  found  in  fresh  water,  those  belonging  to  the 
families  of  desmids  and  diatoms  are  most  interest- 
ing. We  have  already  spoken  ot  plants  consisting 
of  one  cell,  and  these  also  consist  of  one  cell ;  but 
they  have  this  peculiarity,  that  their  cells  are 
divided  into  two  equal  parts,  each  part  having  the 
same  form  as  the  other.  The  desmids  are  dis- 


MICROSCOPE   AT  THE   POND-SIDE.  59 

tinguished  from  the  diatoms  by  their  bright-green 
colour,  and  by  their  cells  not  depositing  silex,  or 
flinty  matter,  as  is  the  case  with  the  latter.  The 
siliceous  nature  of  the  shells  of  diatoms  is  made 
apparent  by  their  not  being  acted  on  by  strong 
acids,  as  nitric  and  hydrochloric. 

The  desmids  sometimes  abound  in  ditches  and 
small  pieces  of  standing  water.  Amongst  other 
objects  in  a  drop  of  water  they  are  easily  recog- 
nized by  their  beautiful  bilateral  forms  and  dark- 
green  colour.  One  o-f  the  most  charming  of  these 
is  named  Euastrum,  and  consists  of  two  notched 
halves  of  a  bright-green  colour,  with  darker  green 
spots.  It  is  represented  at  figure  28,  plate  2. 
The  green  matter  is  composed  of  a  waxy  substance, 
called  chlorophyle,  and  is  the  same  matter  as  that 
which  produces  the  green  colour  of  leaves.  Some 
of  the  desmids  assume  a  lunate  form,  and  are 
named  Closterium,  a  species  of  which  is  figured 
at  29,  plate  2.  There  are  various  species  of  Clo- 
sterium,  all  of  the  same  general  form,  and  occa- 
sionally occurring  in  very  great  abundance.  Some- 
times several  of  the  cells  are  attached  together, 
forming  a  long  chain,  as  in  the  genus  Desmidium, 
seen  at  figure  30,  from  which  the  family  takes  its 
name.  These  break  up  and  go  on  growing.  When 
they  grow,  the  new  cells  are  formed  between  the 
two  halves  of  the  parent  cells.  This  is  represented 
at  figures  136  and  137,  plate  5.  In  a  genus 
called  Scenedesmus,  several  cells  are  united,  and 
the  two  last  halves  are  furnished  with  horns,  as 
seen  at  figure  32  ;  at  other  times  several  cells 
unite,  forming  a  globular  mass,  as  in  Pediastrum, 
represented  at  figure  31.  In  this  case  each  cell 
presents  two  projections,  forming  objects  of  singular 
beauty. 

The    diatoms    are    more    numerous    and   widely 


60  A  HALF-HOUK   WITH    THE 

diffused  than  the  desmids.  The  lattei  are  decom- 
posed, and  their  bodies  perish  when  they  die  ;  but 
from  the  fact  that  the  diatoms  deposit  silex  in 
their  structure,  they  are  almost  imperishable.  They 
are  found  in  great  abundance  in  the  mud  of  rivers, 
ponds,  and  lakes.  They  are  also  present  in  those 
deposits  of  clay  which  once  formed  the  bed  of 
rivers  and  lakes,  and  which  are  now  dry.  In 
order  to  procure  the  diatoms  from  these  deposits, 
ihe  clay  or  earth  should  be  well  washed  with  pure 
water,  and  the  deposit  allowed  to  subside,  and  the 
water  poured  off.  This  may  be  repeated  several 
times.  The  deposit  is  then  to  be  washed  with 
hydrochloric  acid,  and  when  the  effervescence  is 
over,  the  acid  is  poured  off,  and  a  fresh  portion  is 
added.  This  may  be  repeated  several  times,  and 
when  the  hydrochloric  acid  ceases  to  act,  nitric 
acid  may  be  employed  in  the  same  manner.  When 
no  action  occurs  by  its  use  cold,  the  deposit  may 
be  transferred  to  a  watch-glass,  and  kept  over  a 
spirit-lamp,  at  a  temperature  of  about  200°,  for 
three  or  four  hours.  The  deposit  must  then  be 
well  washed  with  pure  water,  to  remove  all  the 
acid.  The  deposit  will  be  found  now  to  consist 
almost  entirely  of  diatoms.  If  anything  else  be 
found,  it  will  be  grains  of  sand.  By  casting  the 
deposit  into  a  small  quantity  of  water,  and  allow- 
ing the  heaviest  particles  alone  to  subside,  these 
will  be  generally  found  to  contain  the  sand  and 
larger  diatoms.  By  repeating  this  process  suc- 
cessively, the  deposits  consist  gradually  of  smaller 
and  smaller  diatoms,  which  may  be  examined  with 
gradually  higher  powers,  in  proportion  to  their 
minuteness.  Some  are  perfectly  round,  as  in  the 
case  of  the  genus  Coscinodiscus,  a  species  of  which 
is  figured  at  38,  plate  2.  It  is  marked  beautifully 
over  their  surface ;  others  are  triangular  :  some  are 


MICROSCOPE    AT    THE   POND-SIDE.  61 

square,  and  attached  together.  The  last  form  is 
seen  in  Melosira,  species  of  which  are  figured 
at  36  and  37,  plate  2,  and  139,  plate  5.  The 
most  common  forms  are  those  which  are  oval,  or 
boat-shaped,  and  represented  by  species  of  Pin- 
nularia  and  Navicula  in  figures  34  and  35  a,  in 
plate  2.  Some  of  these  are  again  larger  at  one 
end  than  the  other,  as  in  Surirella,  figure  33. 
The  markings  upon  the  surface  are  very  various. 
In  some  forms  the  markings  are  exceedingly 
minute  :  so  small  are  they,  that  certain  species 
of  diatoms  have  been  used  as  test  objects,  for 
testing  the  highest  powers  of  the  Microscope. 

Whilst  living,  the  diatoms  possess  the  power  of 
moving  about,  and  in  some  of  them,  as  well  as  the 
desinids,  a  movement  has  been  observed  of  the 
small  particles  in  their  interior.  The  diatoms  are 
generally  of  a  brownish  or  brownish-yellow  colour, 
which  seems  to  be  due  to  a  small  quantity  of  iron 
in  their  composition.  They  are  increased  in  the 
yame  way  as  the  desmids,  by  the  production  of  new 
cells  between  the  parent  frustules.  This  process 
is  seen  in  figure  3o,  a  and  &,  in  plate  2.  The 
continuance  of  the  species  in  these  organisms  is 
secured  by  the  process  of  conjugation  and  the  sub- 
sequent formation  of  the  spores.  This  process  is 
exhibited  in  figures  13o  and  136,  plate  5.  In  some 
cases,  however,  the  spore  is  found  without  the  union 
of  two  cells,  as  in  Melosira  represented  at  figure  137, 
plate  5. 

Sometimes,  attached  to  the  bottom  of  a  pond  or 
river,  or  growing  from  immersed  objects,  or  floating 
about  in  the  water,  will  be  found  long  green  fila- 
ments. These  are  the  fronds  of  confervse.  All 
forms  of  these — and  they  are  very  numerous — will 
be  found  most  beautiful  objects  for  examination. 
They  may  be  laid  on  a  slip  of  glass  in  water,  and 


€  A  HALF-HOUR   WITH   THE 

covered  over  with  a  piece  of  thin  glass ;  or  they 
may  be  placed  in  the  animalcule-cage.  They  con- 
sist of  a  series  of  cells  growing  end  to  end,  and 
their  partition- walls  can  be  easily  seen.  They  are 
of  a  green  colour,  from  the  chlorophyle  contained 
in  their  interior.  In  the  case  of  the  yoke-threads, 
the  chlorophyle  is  frequently  arranged  in  a  spiral 
manner  along  the  interior  of  the  filament,  as  in  the 
Zyynema  represented  at  figure  11,  plate  1.  These 
yoke-threads  may  be  often  seen  to  unite  with  each 
other,  and  the  contents  of  one  cell  are  emptied  into 
the  other,  forming  the  spore  of  the  plant,  as  seen 
at  figure  135,  plate  o.  The  cell  contents  some- 
times break  up  into  smaller  portions,  called 
zoospores,  which,  when  they  escape  from  the  cell  in 
which  they  are  contained,  move  about  with  great 
rapidity.  This  is  seen  in  figure  11,  plate  1,  at 
a  and  b.  The  moving  power  of  the  lower  plants 
is  well  seen  in  the  division  of  these  confervse,  called 
Osdtiatorias,  which  are  sometimes  found  in  semi- 
putrid  water.  A  species  is  figured  at  12,  plate  1. 
As  they  lie  upon  the  glass  slide  they  will  be  seen 
to  move  over  each  other  in  all  directions  :  hence 
their  name. 

Some  of  the  spores  formed  by  the  confervse  move 
about  by  the  agency  of  little  organs  called  cilia. 
These  are  extensions  of  the  motile  matter  of  the 
cell,  and  are  found  very  commonly  in  the  animal 
kingdom.  Occasionally,  a  number  of  these  ciliated 
spores  are  aggregated  together,  forming  a  rapidly- 
moving  sphere.  Of  this  the  Pandorina  Moruni 
affords  a  good  example,  seen  at  figure  13,  plate  1, 
in  which  each  spore  possesses  two  cilia.  But  the 
most  remarkable  of  this  kind  of  moving  plant  is  the 
Volvox  globator,  represented  in  figure  14  of  the 
same  plate.  This  beautiful  moving  plant  was  at 
one  time  thought  to  be  an  animalcule,  but  it  is  now 


MICROSCOPE   AT   THE    POND-SIDE.  63 

regarded  as  a  true  plant.  It  consists  of  a  large 
number  of  spores,  or  cells,  each  having  two  cilia, 
and  connected  together  by  a  delicate  network  of 
threads.  In  the  interior  of  this  moving  sphere  are 
seen  smaller  globular  masses,  of  a  dark-green  colour, 
which  are  the  young  of  the  volvox,  which  have  not 
yet  developed  the  network,  by  means  of  which  their 
spores  are  separated,  and  their  ciliated  ends  pre- 
sented to  the  water,  and  by  means  of  which  their 
movements  are  effected. 

Another  form  which  is  now  regarded  as  a  loco- 
motive plant  is  the  Euglena  viridis,  seen  at  figure 
15,  plate  1.  It  is  often  found  in  prodigious  num- 
bers, giving  to  "water  the  appearance  of  green-pea 
soup.  When  placed  under  the  Microscope,  it  fre- 
quently presents  a  red  speck,  or  point,  at  one  end, 
and  an  elongated  tail  at  the  other.  The  red  spot 
has  been  regarded  as  an  eye  ;  but  if  it  is  watched, 
it  will  be  found  the  red  colour  will  often  extend 
from  the  red  spot  to  the  rest  of  the  body  ;  and  it 
is  probable  that  the  red  colour  is  only  a  change  in 
the  condition  of  the  chlorophyle  contained  in  its 
interior.  Amongst  this  class  of  plants  it  is  not 
unfrequent  for  the  chlorophyle  to  assume  a  red 
colour  at  certain  stages  of  its  growth. 

The  transition  from  the  filamentous  to  the  mem- 
branous form  of  these  plants  is  well  seen  in  the 
species  of  Viva.  These  are  found  in  both  fresh  and 
sea  water.  In  the  early  stages  of  its  growth,  the 
ulva  presents  the  filamentous  form  of  a  conferva, 
as  seen  at  a,  in  figure  26,  plate  2.  Gradually  the 
cells  of  the  filament  split  up  into  two  or  three 
seams  (b) j  and  this  goes  on  till  at  last  a  broad  flat 
membrane  is  produced  (c). 

If  the  plants  of  our  fresh  waters  are  interesting, 
not  less  so  are  the  animalcules ;  for,  just  as  we 
have  one -celled  plants  so  we  have  one-celled  ani- 


64  A  HALF-HOUR    WITH    THE 

mals,  and  it  was  only  by  the  aid  of  the  Microscope 
that  they  were  discovered  and  can  be  examined. 
Wherever  the  above  plants  are  found,  there  will 
also  be  discovered  animals  to  feed  upon  them.  The 
animal  is  distinguished  from  the  plant  by  its  feed- 
ing  on  plants,  whilst  the  latter  feed  on  inorganic 
substances. 

There  is  considerable  difficulty  in  at  once  dis- 
tinguishing between  the  lowest  forms  of  animals 
and  plants.  Although  the  animal  generally  pos- 
sesses a  mouth,  and  a  stomach  in  which  to  digest 
its  vegetable  food,  there  are  some  forms  of  animal 
life  so  simple  as  not  to  possess  either  of  these 
organs.  In  the  sediment  from  ponds  and  rivers 
there  will  frequently  be  found  small  irregular 
masses  of  living,  moving  matter.  If  these  are 
watched,  they  will  be  found  to  move  about  and 
change  their  form  constantly.  As  they  press  them- 
selves slowly  along,  small  portions  of  vegetable 
matter,  or  occasionally  a  diatom,  mix,  apparently, 
with  their  substance.  Cells  are  produced  in  their 
interior,  which  bud  off  from  the  parent,  and  lead 
the  same  life.  These  creatures  are  called  amsebas, 
and  are  represented  in  our  first  plate,  figure  16. 
Although  they  have  no  mouth  or  stomach,  they  are 
referred  to  the  animal  kingdom.  They  appear  to 
consist  entirely  of  the  formative  matter  found  in 
the  interior  of  all  cells  called  moto  planes  or 
sarcode  without  any  cell-wall.  If  we  suppose  an 
amoeba  to  assume  the  form  of  a  disk,  and  to  send 
forth  tentacles,  or  minute  elongated  processes  from 
all  sides,  v:e  should  have  the  sun  animalcule 
(ActinopJirys  Sol),  which  is  represented  at  figure 
17,  plate  1.  This  curious  creature  has  the  power, 
apparently,  of  suddenly  contracting  its  tentacles, 
and  thus  leaping  about  in  the  water.  It  can  also 
contract  its  tentacles  over  particles  of  starch  and 


MICROSCOPE   AT   THE   POND -SIDE.  65 

animalcules,  and  press  them  into  the  fleshy  sub- 
stance in  its  centre.  This  is  undoubtedly  an  animal, 
but  it  has  no  mouth  or  stomach.  A  large  number 
of  such  forms  present  themselves  under  the  Micro- 
scope. Some  of  them  are  covered  with  an  external 
envelope,  which  they  make  artificially,  by  attaching 
small  stones  and  other  substances  to  their  external 
surface,  as  in  the  case  of  the  Difflugiae,  seen  at 
figure  18,  plate  1  ;  or  they  may  form  a  regular 
case,  or  carapace,  consisting  of  a  hairy  membrane, 
as  in  Arcella,  represented  at  figure  19.  We  shall 
meet  again  with  forms  resembling  these  when  wo 
take  our  Microscope  to  the  sea- side. 

One  of  the  most  common  animalcules  met  with 
in  fresh  water,  and  whose  presence  can  easily  be 
insured  by  steeping  a  few  stalks  of  hay  in  a  glass 
of  water,  is  the  bell-shaped  animalcule.  These 
animalcules,  which  are  called  Vorticetta,  are  of 
various  sizes.  Some  are  so  large  that  their  presence 
can  easily  be  detected  by  the  naked  eye,  whilst 
others  require  the  highest  powers  of  the  Micro- 
scope. They  are  all  distinguished  by  having  a 
little  cup-shaped  body,  which  is  placed  upon  a  long 
stalk,  figured  at  40,  in  our  second  plate.  The  stalk 
has  the  peculiar  power  of  contracting  in  a  spiral 
manner,  which  the  creature  does  when  anything 
disturbs  it  in  the  slightest  manner.  In  some  species 
these  stalks  are  branched,  so  that  hundreds  of  these 
creatures  are  found  on  a  single  stem,  forming  an 
exceedingly  beautiful  object  with  the  Microscope. 
The  stalks  of  these  compound  vorticellse  are  con- 
tracted together,  so  that  a  large  mass,  expanding 
over  the  whole  field  of  the  Microscope,  suddenly 
disappears,  and,  "  like  the  baseless  fabric  of  a  vision, 
leave  not  a  wrack  behind."  A  little  patience, 
however,  and  the  fearful  creatures  will  once  more 
be  seen  to  expand  themselves  in  all  their  beauty. 


66  A   HALF-HOUR   WITH   THE 

The  mouth  of  their  little  cup  is  surrounded  by  cilia, 
which  are  in  constant  movement  j  and  when  ex- 
amined minutely,  they  will  be  found  to  possess  two 
apertures,  through  one  of  which  currents  of  water 
pass  into  the  body,  and  from  the  other  pass  out. 
Not  unfrequently  the  cup  breaks  off  its  stalk.  It 
then  contracts  its  mouth,  and  proceeds  to  roll  about 
free  in  the  water.  Many  other  curious  changes  in 
form  and  condition  have  been  observed  in  these 
wonderful  bell-shaped  animalcules. 

If,  now,  we  go  to  a  very  dirty  pond  indeed,  into 
which  cesspools  are  emptied,  and  dead  dogs  and 
cats  are  thrown,  we  shall  find  abundant  employ- 
ment for  our  Microscope  in  the  beautiful  forms  of 
animalcules  which  are  placed  by  the  Creator  in 
these  positions  to  clear  away  the  dirt  and  filth,  and 
prevent  its  destroying  the  life  of  higher  animals. 
In  such  waters,  amongst  a  host  of  minor  forms,  we 
are  almost  sure  to  meet  with  the  magnificent  Para- 
mcecium  Aurelia,  figured  at  39,  plate  2.  He  moves 
about  the  water  a  king  amongst  the  smaller  prey, 
on  whom  he  feeds  without  ceasing.  He  is  of  an 
oblong  form,  covered  all  over  with  cilia,  and  very 
rapid  and  active  in  his  movements,  as  able  to  dart 
backwards  as  forwards,  and  turning  round  with  the 
greatest  facility.  In  his  inside  several  spots  are 
observed.  If  a  little  indigo  or  carmine  is  intro- 
duced into  the  water  in  which  he  lives,  these  spots 
become  coloured  by  his  taking  up  these  substances. 
From  this,  Ehrenberg  concluded  that  these  spots 
were  stomachs,  and  as  such  spots  are  very  common 
amongst  these  animalcules,  he  called  them  many- 
stomached  (Polygastrica).  There  is,  however, 
reason  to  doubt  the  correctness  of  this  conclusion 
of  the  great  microscopist,  as,  although  these  spots 
exist  in  the  body,  they  are  not  necessarily  stomachs. 
They  are,  in  fact,  empty  spaces,  or  vacuoles  in  the 


MICEOSCOPE   AT   THE   ?OND-SIDE,  67 

interior  of  the  little  fleshy  lump  of  which  the  ani- 
mal is  composed.  They  are  found  in  the  vorticella, 
and  in  most  of  the  true  animalcules. 

All  animalcules  have  been  called  infusory,  be- 
cause they  seem  so  abundant  in  many  kinds  of 
vegetable  infusions.  Ehrenberg  divided  them  into 
Polygastric  and  RotifeTous.  The  last  are  also  called 
wheel-animalcules,  as,  when  looked  at  through  the 
Microscope,  they  appear  to  be  supplied  with  little 
wheels  on  the  upper  part  of  their  body.  The  most 
common  form  of  these  creatures  is  the  Rotifer 
vulgaris,  represented  at  figure  41,  plate  2.  The 
branches  or  leaves  of  any  of  our  common  water- 
plants  can  scarcely  be  examined  without  some  of 
those  pretty  little  creatures  being  found  nestling 
among  them.  The  structure  of  these  creatures  is 
highly  complicated,  and  the  family  to  which  it 
belongs  is  far  removed  from  the  poly  gastric  ani- 
malcules with  which  it  is  associated  by  Ehrenberg. 
On  examination,  the  wheels  will  be  found  to 
consist  of  two  extended  lobes,  the  edges  of  which 
are  covered  with  cilia.  These  cilia  are  in  a  con- 
stant state  of  movement,  and  produce  the  appear- 
ance of  wheels  moving  on  an  axis.  Between  the 
wheels  is  the  entrance  to  the  mouth,  which,  in 
many  species  of  wheel-animalcules,  is  furnished  with 
a  strong  pair  of  jaws.  This  leads  to  an  oesophagus, 
a  stomach,  and  an  intestinal  tube.  Two  little  spots 
on  the  neck  seem  to  indicate  the  existence  of  eyes ; 
whilst  a  projecting  organ,  believed  to  be  analogous 
to  the  antennae,  or  feelers  of  insects,  is  seen 
directly  below  them.  The  tail  is  finished  off  with 
a  pair  of  little  nippers,  by  which  the  creature  has 
the  power  of  attaching  itself  to  objects.  When 
moving,  its  whole  body  is  extended,  but  it  has  the 
power  of  drawing  itself  up  like  a  telescope  in  its 
case,  and  appearing  almost  round. 
P  2 


68  A   HALF-HOUR   WITH   THE 

The  wheel-animalcules  abound  in  our  ponds  and 
rivers,  and  sometimes  occur  in  great  numbers  in 
the  aquarium.  The  common  wheel-animalcule, 
Rotifer  vulgaris,  is  most  frequently  found  in  lead 
gutters  and  the  drinking-fountains  used  for  birds. 
If  a  little  of  the  deposit  which  usually  accumu- 
lates in  the  former  is  placed  in  a  test-tube  with 
water,  and  exposed  to  the  light,  in  a  short  time  the 
rotifers  will  be  found  swimming  about  in  great 
numbers,  and  may  be  transferred  to  a  live-box  by 
means  of  a  dipping-tube  :  if  allowed  to  dry,  they 
can  be  afterwards  revived  by  adding  a  little  water. 
Several  of  the  wheel-animalcules  are  fixed,  forming 
on  the  outside  of  their  bodies  a  little  case  or  tube 
in  which  they  dwelh  These  forms  are  beautifully 
seen  when  illuminated  by  the  spot  lens. 


MICROSCOPE  AT   THE   SEA-SIDF.  69 


CHAPTER    V. 

A  HALF-HOUB  WITH  THE  MICEOSCOPE 
AT  THE  SEA-SIDE. 

ON  a  visit  to  the  sea-side,  the  Microscope  is  an 
essential  instrument  to  all  who  would  wish  to 
study  the  wonders  of  the  ocean.  It  is  a  curious 
fact,  that  the  few  grains  of  common  salt  in  the 
gallon  of  sea-water  seem  to  determine  the  exist- 
ence of  thousands  of  plants  and  animals.  We  shall 
therefore  find  living  in  the  sea-water,  plants  and 
animals  belonging  to  the  same  families  as  those 
in  fresh  water,  but  belonging  to  entirely  different 
species. 

The  sea-weeds  present  strikingly  different  forms. 
Although  many  of  them  are  microsopic,  and  belong 
to  the  families  of  Diatomacece  and  Confervacece,  all 
the  larger  forms  present  interesting  objects  for 
examination  in  the  structure  of  their  fruit-bearing 
organs.  No  better  subject  for  the  latter  purpose 
can  be  procured  than  the  common  bladder-wrack, 
which  is  so  abundant  on  all  our  shores.  If  a  frond 
of  this  fucus  is  examined,  there  will  be  found  at 
certain  parts  a  swollen  mass,  dotted  over  with 
round  yellowish  bodies.  If  one  of  these  is  taken 
and  carefully  pressed  between  two  pieces  of  glass, 
it  will  present  the  spores  surrounded  with  hairs 
of  the  most  delicate  and  various  structure.  Some  of 
the  spores  are  divided  into  four  parts,  and  on  this 
account  are  called  tetraspores.  These  are  seen  at 
d,  figure  111,  plate  4.  The  bladder-wrack  is  fre- 
quently covered  with  minute  parasites ;  one  of  the 
most  common  of  these  is  Polysiphonia  fastigialcl, 


70  A  HALF-HOUR  WITH   THE 

which  is  represented  at  figure  111,  plate  4.  As 
seen  in  the  drawing,  this  little  plant  is  branched, 
and  the  stems  present  a  series  of  flattened  cells. 
On  the  branches  are  placed  the  fruit-bearing 
organs,  in  the  form  of  little  capsules,  seen  at  a. 
These  capsules  contain  tetraspores  (d).  At  the 
ends  of  the  branches  are  organs  of  another  kind, 
representing  the  stamens,  and  which  are  called 
antheridia.  These  are  seen  at  e  in  the  same  figure. 
The  sea-weeds  present  a  great  variety  in  the  form 
of  these  organs,  and  may  be  easily  preserved  for 
investigation  in  small  glasses  of  sea-water. 

The  animal  structures  of  the  sea-water  must 
now,  however,  claim  our  attention.  Amongst  the 
lowest  form  of  animal  life  are  the  sponges.  They 
are  frequently  cast  on  the  shore  with  sea-weeds, 
and  afford  interesting  objects  for  the  Microscope. 
They  are  composed  of  animal  matter,  which  lies 
upon  a  structure  of  horny,  calcareous,  or  sili- 
ceous matter.  The  common  sponge  which  is  used 
for  domestic  purposes  may  be  taken  as  a  type  of  the 
whole  group.  If  a  thin  section  of  the  common 
sponge  is  made  with  a  pair  of  sharp  scissors  and 
placed  under  a  low  power,  it  will  be  seen  to  be 
composed  of  a  network  of  horny  matter,  repre- 
sented in  figure  140,  plate  5.  If  now  we  take  one 
of  the  common  forms  from  our  own  sea-shore,  we 
shall  find  that  the  network  is  composed  of  sili- 
ceous spicules  lying  one  over  the  other,  as  repre- 
sented in  figure  141  of  plate  5.  If  one  of  these 
spicules  is  examined  (a)  and  compared  with  a 
spicule  from  another  sponge,  it  will  be  found  to 
differ  in  form  and  size ;  and  the  species  of  sponges 
can  actually  be  made  out  by  the  shape  of  their 
spicules.  Some  of  our  British  sponges  have  cal- 
careous spicules.  This  is  the  case  with  Grantia 
ciliata.  There  is  a  little  boring  sponge,  called 


MICROSCOPE   AT   THE   SEA-SIDE.  71 

Cliona,  found  in  the  shells  of  old  oysters,  which 
has  its  spicules  pin-shaped,  as  seen  at  figure  142. 
The  fresh-water  sponge  has  very  peculiar-shaped 
spicula,  and  is  represented  at  figure  143.  In  some 
the  siliceous  bodies  are  round,  with  projections, 
as  in  Tetliea,  seen  in  the  drawing,  figure  145. 
Sometimes  the  spicula  assume  a  stellate  form, 
and  are  even  branched,  as  in  the  spicula  of  an 
unknown  sponge  given  at  figure  144. 

Amongst  the  lowest  forms  of  animal  life,  none 
are  more  interesting  to  the  microscopic  observer 
than  those  belonging  to  the  family  of  Foramini- 
fera  (Hole-bearers).  They  are  thus  called  on 
account  of  the  minute  holes  which  cover  their 
shells.  If  we  suppose  a  creature  as  simple  in 
structure  as  the  amoeba,  or  sun  animalcule,  of  which 
we  have  previously  spoken,  and  which  are  figured 
in  16  and  17,  plate  1,  with  the  power  of  forming 
a  little  calcareous  shell,  we  should  have  a  foramini- 
fer.  Some  of  these  shells  have  the  form  of  a 
nautilus,  and  when  first  observed  they  were  sup- 
posed to  belong  to  this  group  of  shell-fishes.  In 
form  they  certainly  resemble  the  higher  forms  of 
mollusca,  as  may  be  observed  in  figures  21  and  24, 
in  plate  1.  Sometimes,  however,  they  are  elon- 
gated or  cone-shaped,  as  in  figure  25.  Other  forms 
are  seen  in  figures  20  and  22.  They  may  often 
be  found  alive  -at  the  sea-side,  nestling  in  the  roots 
of  the  gfgantic  tayles  which  are  so  often  thrown 
on  the  shore  after  a  storm.  If  the  roots  of  these 
plants  (Laminarice)  are  washed,  and  the  deposit 
examined  carefully,  the  foraniinifera  will  be  seen 
at  the  bottom  of  the  vessel,  and  may  be  picked 
out  one  by  one.  When  this  is  done,  they  will  be 
found  to  have  the  power  of  protruding  through  the 
little  holes  in  their  shells  their  soft  bodies,  in  the 
form  of  long  tentacles,  as  seen  at  figure  24,  in  the 


?  2  A   HALF-HOUR   WITH   THE 

first  plate.  With  these  they  seem  to  have  the 
power  of  moving,  as  well  as  of  taking  up  the 
matters  by  which  they  are  nourished.  The  shells 
of  these  creatures  are  not  so  small  but  they  may 
be  seen  with  the  naked  eye,  and  they  need  only  a 
low  power  to  observe  all  their  structure.  They  are 
found  at  great  depths  in  the  ocean,  and  have  been 
brought  up  by  the  dredge  from  the  deepest  parts  of 
the  Atlantic.  They  are  very  abundant  in  some 
rocks,  especially  in  the  chalk  :  they  may  be  ob- 
tained from  the  latter  substance  by  rubbing  a  piece 
of  chalk  with  a  brush  in  water.  The  water  must 
be  first  decanted  from  the  coarser  particles  of  chalk, 
and  in  subsequent  deposits  the  foraminifera  will  be 
found.  They  may  be  obtained  from  dry  sand  in 
which  they  are  contained,  by  throwing  the  sand 
into  water,  when  the  sand  will  si'nk  and  the 
foraminifera  will  swim  on  the  surface,  and  may  be 
skimmed  off.  They  are  best  examined  as  opaque 
objects. 

The  family  of  polyps  will  next  command  atten- 
tion. One  of  the  most  simple  forms  of  this  family 
is  found  in  ponds  and  rivers,  and  is  called  the 
fresh-water  polyp  or  hydra.  It  is  figured  at  146, 
plate  5.  It  may  be  easily  observed,  adhering  to 
plants,  with  the  naked  eye,  and  needs  only  a  low 
power  with  transmitted  light  to  observe  it  accu- 
rately. Its  body  is  cup-shaped,  surmounted  with 
eight  long  tentacles,  which  it  has  the  power  of  re- 
tracting. It  produces  young  ones  by  the  process  of 
budding,  and  the  buds  may  be  often  seen  protrud- 
ing from  the  side  of  their  parents.  It  is  very 
tenacious  of  life,  and  may  be  cut  into  several  pieces, 
and  each  part  will  grow  into  a  new  hydra.  These, 
with  many  other  polyps  and  the  jelly-fish,  have  their 
flesh  filled  with  little  hair-like  bodies,  which,  from 
their  property  of  stinging  in  some  species,  have 


PLATE  6. 


MICROSCOPE   AT   THE    SEA-SIDE.  73 

been  called  stinging  hairs,  as  seen  at  a,  figure  14G. 
If  we  suppose  several  of  these  hydras  placed  in 
little  cups  upon  a  common  branch  or  stem,  we 
should  have  a  Sertularia,  or  such  an  animal  as  is 
represented  at  Figure  147,  Plate  5.  These  polyps 
are  very  common  on  all  our  sea-shores  j  and  the 
branches  and  cups  are  often  cast  up  on  the  shore, 
and  regarded  by  the  uninstructed  as  sea-weeds. 
The  branches  and  cups  are  called  the  polypidoms  of 
the  animal,  and  assume  a  great  variety  of  forms. 
When  the  cups  are  fixed  on  ringed  stalks,  they 
constitute  the  genus  Campanularia,  seen  at  figure 
148,  plate  5.  These  cups  are  often  objects  of  great 
beauty,  as  in  those  of  Campanularia  volubilis, 
figured  in  149.  It  is  the  polypidom  which  consti- 
tutes the  coral  in  the  family  of  polyps,  producing 
the  masses  of  carbonate  of  lime  which  sometimes 
cover  the  bottom  of  the  ocean  and  form  reefs  in  the 
sea.  In  one  family  of  polyps,  known  as  sea-fans 
(Gforgoniai),  which  are  calcareous,  the  fleshy  mass 
covering  the  horny  polypidom  contains  spicula  of 
various  forms,  which  are  beautiful  objects  under  the 
Microscope.  These  spicula  are  seen  at  figure  150, 
plate  5.  The  red  coral  of  commerce  is  another 
interesting  form  of  these  polypidoms.  In  some 
families  of  these  polyps,  as  in  the  campanularidse 
and  the  corynidse,  the  young,  before  they  arrive 
at  their  mature  stage,  assume  the  forms  of  minute 
medusae  or  jelly-fishes.  These  are  exceedingly 
beautiful  objects  for  microscopic  observation. 

Another  family  of  animals  common  enough  in 
the  sea,  are  the  star-fishes  and  sea-eggs  (Echinoder- 
mata).  Although  not  themselves  microscopic, 
certain  parts  of  their  structure  present  very  in- 
teresting objects  for  examination.  If  a  section  is 
made  of  one  of  the  spines  of  the  common  echinus, 
or  sea- egg,  it  presents  under  a  low  power  a  beau- 


74  A   HALF-HOUR    WITH   THE 

tifully  radiated  structure.  This  is  seen  at  figure 
151,  plate  5.  The  suckers,  also,  of  the  same  animal 
present  little  rosettes,  surrounded  by  a  very  delicate 
hyaline  disk,  represented  at  figure  152.  Upon  the 
surfaces  of  both  star-fishes  and  sea-eggs  will  be 
found  little  inoveable  bodies  which  are  called  pedi- 
cettarice.  In  the  sea-egg  they  pos&ess  three  moveable 
nipper-like  limbs,  whilst  in  the  common  star-fish 
they  present  only  two.  These  are  represented  at 
figures  153  and  154,  plate  5.  A  controversy  has 
been  raised  on  the  question  as  to  whether  these 
bodies  are  parasitic  animals,  or  part  and  parcel  of 
the  structure  of  the  creature  on  which  they  are 
found.  As  they  are  so  constantly  present,  they  are 
undoubtedly  parts  of  the  animal  on  which  they  are 
found.  The  movements  of  the  nippers  are  very 
active,  and  they  frequently  lay  hold  of  objects 
which  pass  near  them. 

As  common  on  the  shore  as  the  polypidoms  of 
the  polyps,  are  the  animal  skeletons  called,  in  some 
parts  of  the  country,  sea-mats  (Flustra  foliaceci). 
"When  placed  under  a  low  power,  and  viewed  by 
reflected  light,  the  sea-mat  is  composed  of  little 
cavities  or  cells,  seen  at  figure  162,  plate  6.  In 
each  one  of  these  is  seated  a  creature  of  much  more 
complicated  organization  than  the  polyps  just  ex- 
amined. It  has,  it  is  true,  a  ring  of  tentacles  ;  but 
if  these  are  examined,  the  tentacles  are  found  to  be 
covered  with  cilia,  as  seen  at  a,  in  figure  163, 
plate  0.  This  family  of  creatures  are  called  Polyzoa, 
or  Eryozoa,  and  form  a  group  of  animals  which  are 
classed  with  the  Mollusca,  or  shell-fish.  Sometimes 
these  creatures  attach  themselves  to  sea- weeds, 
oysters,  stones,  and  other  objects  at  the  bottom  of 
the  sea,  forming  a  kind  of  cellular  membranous 
expansion.  Such  are  the  species  of  Lepralia, 
figured  at  155.  Sometimes  the  cells  are  elongated 


MICROSCOPE   AT   THE   SEA-S1DF.  75 

and  elevated  above  the  surface  of  the  object  on 
which  they  are  placed,  as  in  the  case  of  Bowerbankia, 
seen  at  156.  A  beautiful  form  of  these  creatures 
is  the  shepherd's-purse  coral  (Notamia  bursarici), 
represented  at  figure  157.  This  creature  belongs 
to  a  group  of  the  polyzoa,  remarkable  for  possess- 
ing little  processes  on  the  margins  of  their  cells,  in 
shape  resembling  the  bowls  of  tobacco-pipes,  birds' 
bills,  and  bristle-like  organs.  On  examining  them 
with  the  Microscope,  they  present  a  very  compli- 
cated organization.  The  birds'  bills  possess  two 
jaw-like  processes,  which  open  and  shut  like  a  bird's 
beak,  and  from  this  fact  they  have  been  called  avicu- 
laria,  or  bird's-head  processes  (a).  The  tobacco-pipe 
form  in  Notamia  is  peculiar  to  that  genus.  In 
other  species,  as  in  Eugula,  avicularia,  seen  in 
figure  158,  these  creatures  possess  not  only  the 
bird's-head  process,  but  a  second,  consisting  of  a 
long  bristle  or  seta,  attached  by  a  joint  to  a  process 
below  (a).  These  bodies  are  called  vibracula,  and 
the  bristle-like  extremity  is  kept  constantly  in 
action,  and  the  form  of  avicularia  is  seen  in  Bugula 
Murrayana,  at  figure  159.  Both  processes  are  seen 
in  Scrupularia  scruposa,  at  figure  160.  Few  objects 
are  more  curious  under  the  Microscope  than  these 
avicularia  and  vibracula  in  a  state  of  action. 
Whilst  the  function  of  the  vibracula,  seen  at  a, 
figure  160,  seems  to  be  to  sweep  away  objects 
that  would  interfere  with  the  life  of  the  animal  in 
the  cell,  it  has  been  suggested  by  some  that  the 
avicularia  secure  by  their  jaws  the  food  necessary  for 
its  sustenance  :  it  seems  probable,  however;  that 
they  serve  the  purpose  of  a  protective  police.  Of 
the  various  forms  which  the  cup  itself  assumes, 
none  are  more  interesting  than  those  of  the  snake- 
head  zoophyte,  shown  at  figure  161,  plate  6,  in 
which  it  assumes  the  form  of  a  snake's  head,  with 


76  A  HALF-HOUR   WITH    THE 

the  tentacula  projecting  like  a  many-parted  tongue. 
The  polyzoa  are  also  inhabitants  of  the  fresh  water. 
Of  these  the  most  common  form  is  the  Plumatella 
repens,  figured  at  163.  The  eggs  of  a  fresh-water 
species,  Cristatella  inuced<o,  seen  in  figure  164,  are 
covered  with  projecting  spines  with  double  hooks 
at  their  extremities,  perhaps  for  the  purpose  of 
catching  hold  of  objects.  Such  eggs  may  be  often 
found  upon  portions  of  water-lily,  bulrush,  and 
other  aquatic  plants  which  float  about  in  our  rivers, 
lakes,  and  ponds. 

Although  but  few  of  the  shell-fish  belonging  to 
the  large  class  of  mollusca  are  microscopic,  yet  the 
structure  of  their  shells  can  only  be  investigated 
by  the  aid  of  the  Microscope. 

If  any  common  shell  be  picked  up  on  the  sea- 
shore, it  will  be  found  to  possess  a  rough  outside, 
generally  of  a  darker  colour,  and  sometimes  beauti- 
fully ornamented,  whilst  on  the  inside  it  is  smooth, 
and  frequently  of  a  rose-colour.  This  inner  smooth 
layer  is  called  the  nacre  of  the  shell ;  and  it  is 
from  this  substance  that  pearls  are  formed  in  the 
interior  of  many  shells.  Both  the  outer  and  the 
inner  layers  present  different  kinds  of  structure  in 
different  species  of  shells.  The  outer  layer  can  be 
well  examined  in  the  shell  of  the  mollusc  called  the 
Pinna.  The  outer  layer  in  this  shell  projects  be- 
yond the  inner,  and  may  be  easily  submitted  to 
examination  by  reflected  light  under  a  low  power, 
when  it  will  exhibit  the  appearance  represented  at 
figure  166,  plate  6.  The  external  surface  presents 
the  appearance  of  hexagonal  cellular  tissue.  If  a 
portion  of  the  shell  is  ground  down,  so  as  to  form 
a  very  thin  layer,  it  may  be  examined  with  trans- 
mitted light,  and  its  hexagonal  structure  will  be 
much  more  apparent.  If  a  portion  be  examined 
lengthwise,  it  will  be  seen  that  the  hexagons  result 


MICROSCOPE   AT   THE   SEA-SIDE.  77 

from  the  shell  being  composed  of  a  series  of  hex- 
agonal prisms,  as  seen  in  the  view  of  a  longitudinal 
section  given  at  figure  166,  plate  6. 

All  bivalve  shells  partake,  more  or  less,  of  this 
character ;  and  if  a  portion  of  the  outer  coating  of 
the  shell  of  the  oyster  be  examined,  it  will  be 
found  to  present  a  general  resemblance  to  that  of 
the  shell  of  the  pinna,  as  seen  at  figure  167.  In 
many  shells  the  inner  layer  is  almost  structureless, 
but  in  those  cases  where  the  smooth  white  appear- 
ance is  presented  which  is  called  mother-of-pearl,  it 
consists  of  a  series  of  waved  laminae  lying  irre- 
gularly one  on  the  top  of  the  other ;  represented  at 
figure  169.  In  other  shells  this  membranous  in- 
ternal layer  is  traversed  by  minute  tubes,  as  is  seen 
in  the  genus  Anomia,  seen  at  figure  168.  This 
structure  has  been  considered  clue  to  the  natural 
form  of  the  shell ;  but  late  investigations  lead  to 
the  conclusion  that  these  tubules  are  the  borings  of 
some  parasitic  animal. 

The  shells  of  the  Crustacea  also  present  a  series 
of  very  interesting  structural  differences.  The  shell 
of  the  common  prawn,  when  mounted  in  Canada 
balsam,  or  examined  in  water  or  glycerine,  presents 
a  series  of  bodies  looking  like  nucleated  cells. 
These  are  seen  in  figure  170,  plate  6.  Many 
shells  present  this  appearance,  and  it  was  at  one 
time  supposed  to  indicate  clearly  that  the  shell 
originates  in  cell-growth  as  well  as  other  parts  of 
the  structure  of  an  animal.  It  has  been,  however, 
recently  shown,  that  such  appearances  as  that  pre- 
sented by  the  prawn-shell  may  be  produced  by  the 
crystallization  of  inorganic  salts  in  contact  with 
organic  substances  in  solution,  independent  of  a 
living  organism. 

Surprising  as  it  may  seem  to  some  persons,  the 
teeth  of  mollusca  afford  beautiful  objects  for  mi- 


78  A   HALF-HOUR  WITH   THE 

croscopic  examination.  All  that  is  necessary  to 
examine  these  organs  is,  to  take  the  palate,  or 
tongue,  as  it  is  called,  of  any  of  our  common  mol- 
luscs, and  to  stretch  it  on  a  glass  slide,  when  it  may 
be  seen  by  transmitted  or  reflected  light.  In  the 
common  whelk,  the  teeth  are  placed  in  rows,  and 
are  composed  of  a  broad  base  with  four  projecting 
points,  the  two  outer  of  which  are  larger  than 
the  inner,  as  seen  in  figure  171,  plate  6.  In  the 
limpet,  the  teeth  present  four  projections,  which 
are  all  of  the  same  size  ;  seen  in  figure  172.  In 
the  common  periwinkle  another  kind  of  arrange- 
ment is  observed,  and  is  figured  at  173. 

When  sea-side  specimens  have  been  observed  and 
put  up,  the  fresh-water  mollusca  may  be  next 
investigated.  Here  other  forms  will  be  observed. 
The  species  of  the  genus  Limneus  are  found 
in  every  pond,  and  kept  in  every  aquarium. 
The  tongues  of  these  creatures,  represented  at 
figure  174,  will  give  a  lively  idea  of  the  nature 
of  the  scavengering  processes  they  carry  on . 

The  scales  of  fishes  are  interesting  microscopic 
objects.  The  structure  of  these  organs  indicates 
the  family  of  fishes  to.  which  they  belong.  It  is  in 
this  way  that  a  single  scale  found  in  a  rock  will 
throw  a  light  on  the  nature  of  the  fishes  which 
inhabited  the  seas  or  rivers  from  which  the  rock 
was  deposited. 

Fishes'  scales  have  been  called  ganoid,  placoid, 
cycloid,  and  ctenoid,  according  to  the  families  to 
\vhich  they  belong.  The  sturgeon  has  ganoid 
scales.  They  are  shiny,  and  have  a  structure 
like  bone,  and  are  represented  at  figure  175, 
plate  6. 

The  sharks,  rays,  and  skates  have  placoid  scales. 
They  are  frequently  terminated  with  a  prickle,  as 
in  the  scales  of  the  skate  ;  seen  at;  figure  1 76. 


MICROSCOPE  AT    THE   SEA-SIDE.  <  W 

This  structure  resembles  the  tubular  structure  in 
the  teeth  of  the  higher  animals. 

Fish-scales  are  frequently  permeated  with  minute 
tubes,  drawn  in  figure  177,  plate  6.  These  appear- 
to  be  the  work  of  some  minute  parasite,  such  as 
that  producing  the  tubules  in  shells,  and  which  has 
hitherto  evaded  the  scrutinizing  investigation  of 
the  microscopic  observer. 

The  fishes  of  the  earlier  rocks  belong  to  the 
ganoid  and  placoid  groups.  The  great  majority  of 
recent  fishes  belong  to  the  remaining  groups.  The 
common  sole  affords  an  instance  of  the  ctenoid,  or 
comb-like  scale,  seen  at  figure  178. 

The  cycloid,  or  circular  scales,  are  found  in  such 
fish  as  the  whiting,  and  represented  at  figure  179. 
It  is  not  uncommon  to  find  in  these  scales  cal- 
careous particles,  shown  at  a.  In  the  sprat  the 
cycloid  scale  assumes  a  form  almost  as  broad  as  it 
is  long,  and  is  seen  in  figure  180. 

The  examination  of  these  hard  structures  in  the 
marine  creatures  is  a  good  preparation  for  the 
further  study  of  those  hard  parts  in  the  higher 
animals  to  which  the  name  of  bone  and  ivory  i& 
given.  Such  things  may,  however,  be  procured  in 
the  house ;  and  when  the  rain  is  falling,  the  sea- 
side forsaken,  or  the  country  miserable -looking,  we 
can  still  enjoy  the  long  winter  evenings  with  our 
Microscope  in  the  house. 


80  A    HALF    HOUR    WITH    THE 


CHAPTER    VI. 

A  HALF-HOUR  WITH  THE  MICROSCOPE 
IN-DOORS. 

FOB  amusement  and  instruction  with  the  Micro- 
scope, we  need  scarcely  stir  out  of  our  rooms.  The 
very  hairs  on  our  head  may  be  made  objects  of 
interesting  investigation,  and  especially  if  we  com- 
pare them  with  the  hairs  of  other  animals,  and  the 
appendages  generally  of  the  skin.  The  fine  outer 
coating  of  the  skin  is  composed  of  minute  scales, 
which  are  flattened  cells,  and  may  be  easily  ob- 
served by  scraping  a  portion  of  the  skin  on  to 
a  glass  slide  with  a  drop  of  water  on  it.  The  nails, 
the  hairs,  and  other  appendages  of  the  skin,  are 
composed  of  the  same  kind  of  scales,  or  cells. 
These  cells  are  developed  in  little  pits,  or  follicles, 
from  which  the  hair  is  projected,  as  it  were,  by 
their  growth  from  below.  Under  a  low  power  the 
cells  of  the  human  hair  cannot  be  observed.  It  pre- 
sents, however,  a  well-marked  distinction  between 
the  outside,  or  cortical  layer,  and  the  interior,  or 
pulp.  The  latter,  by  a  high  power,  especially  if 
the  hair  has  been  first  submitted  to  the  action  of 
sulphuric  acid,  will  be  found  to  contain  cells  more  or 
less  spherical,  whilst  the  former  contains  cells  more 
or  less  flattened.  These  project  a  little  beyond  the 
edge  of  the  hair,  so  that  its  sides  are  not  quite 
smooth,  as  seen  at  figure  184  in  plate  7.  By 
placing  a  hair  between  two  pieces  of  cork,  fine 
transverse  sections  of  it  may  be  made  by  means  of 
a  sharp  razor.  If  these  are  put  under  the  Micro- 


London.  "Robert  Hardwicke,  1860. 


MICROSCOPE   IN-DOORS,  81 

scope,  the  pulpy  portions  will  present  a  dark  ap- 
pearance in  the  centre,  as  seen  at  a.  The  hairs  of 
animals  offer  a  great  variety  in  the  disposition  of 
the  cells  of  which  they  are  composed.  The  hairs 
of  the  mouse  present  a  series  of  dark  partitions 
running  across  the  hair  between  the  cells.  In  the 
younger  hairs,  these  partitions  are  single,  as  repre- 
sented at  a  in  figure  185,  plate  7  ;  whilst  in  the 
older  ones  they  appear  double,  as  seen  at  b.  The 
hairs  from  the  ear  of  the  mouse  present  these  dark 
partitions  very  distinctly,  shown  at  d.  Such  hairs 
stand  intermediate  between  true  hair,  a  section  of 
which  is  seen  at  c,  and  wool.  A  -piece  of  flannel  or 
blanket  will  afford  a  good  illustration  of  the  latter. 
This  is  figured  at  235  in  the  8th  plate.  In  this 
case  it  will  be  seen  that  the  scales,  or  cells,  of  the 
cortical  part,  project  beyond  the  surface,  and  render 
the  wool  rough.  This  roughness  of  the  outside  is 
supposed  to  render  such  hairs  fitted  to  be  used  in 
the  process  of  felting  ;  the  rough  sides  of  the  hairs 
adhering  together.  The  chemical  composition  of 
the  hair  has  also  something  to  do  with  this  pro- 
cess. Human  and  other  smooth  hairs,  will  not 
felt. 

The  fibres  of  plants  used  in  weaving  may  be 
conveniently  compared  with  hairs  derived  from  the 
animal  kingdom.  The  woody  fibre  of  the  flax  may 
be  obtained  from  a  linen  handkerchief.  A  linen 
fibre  is  represented  at  6  in  figure  234,  plate  8. 
The  apparent  knots  in  the  fibre  arise  from  injury 
in  the  uses  to  which  the  fabric  has  been  applied. 
The  original  fibres  have  no  such  fractures,  as  shown 
at  a,  and  are  perfectly  smooth.  So  are  the  fibres 
of  silk,  represented  at  figure  236.  Cotton-wool  ia 
produced  from  the  inner  surface  of  the  pod,  or  fruit 
of  the  cotton-plant,  and  is  figured  at  figure  237.  It 
becomes  twisted  during  its  growth,  and  although 


82  A   HALF-HOUR   WITH    THE 

not  so  strong  as  linen  or  silk,  its  irregular  surfaces 
permit  its  being  spun  into  a  strong  yarn,  from 
which  all  cotton  fabrics  are  made.  The  young 
microscopist  should  make  himself  acquainted  with 
the  forms  of  these  various  fibres ;  as,  from  their 
being  so  constantly  present  in  rooms  where  the 
Microscope  is  used,  and  occasionally  employed  in 
cleaning  the  apparatus,  they  often  present  them- 
selves as  foreign  substances,  among  other  objects 
that  are  being  examined. 

It  is  also  interesting,  and  sometimes  of  import- 
ance, to  be  able  to  ascertain  of  what  material  a 
fabric  may  be  composed.  Thus  by  means  of  the 
Microscope,  and  that  alone,  we  know  certainly  that 
the  cere-cloths  in  which  Egyptian  mummies  ara 
wrapped  is  a  linen  fabric,  whilst  the  similar  invest- 
ment of  Peruvian  mummies  is  cotton.  The  hair  of 
the  bat,  represented  at  figure  186,  plate  7,  presents  a 
singular  instance  of  the  projection  of  the  scales,  or 
cells,  in  a  regular  form.  Hairs  are  not  often  perfectly 
round  ; — in  the  peccary  they  are  oval,  as  seen  in 
figure  187,  plate  7.  If  a  transverse  section  of  this 
hair  is  examined,  it  will  be  found  that  the  cortical 
substance  projects  completely  into  the  pulpy  part 
of  the  hair  in  several  places,  so  as  to  break  up  the 
pulp  into  several  separate  sections. 

In  some  cases  it  is  not  easy  to  distinguish 
between  outside  and  inside  structure,  as  seen  in 
the  hair  of  the  musk-deer,  in  which  the  whole  is 
found  to  consist  of  a  mass  of  hexagonal  cellular 
tissue,  similar  to  that  seen  in  the  pith  of  plants. 
This  hair  is  shown  in  plate  7,  figure  188. 

Insects  are  frequently  covered  with  hairs,  espe- 
cially in  their  larva,  or  caterpillar  state.  These 
hairs  when  stiff  and  sharp,  penetrate  the  skin, 
and  produce  irritation  there.  This  is  the  case  with 
the  large  tiger  caterpillar.  The  hairs  of  this  cater- 


MICROSCOPE   IN-DOORS.  83 

pillar  are  furnished  with  a  series  of  barbs,  which, 
when  they  once  penetrate  the  skin,  are  not  easily 
removed,  as  seen  in  figure  189,  plate  7. 

Spiders  are  frequently  covered  with  hairs,  some 
of  which  are  branched,  as  at  a  in  figure  190; 
others  present  a  spiral  appearance,  seen  at  b ; 
whilst,  again,  others  offer  a  series  of  small  bristle- 
like  hairs  running  down  each  side  of  the  primitive 
hair,  which  will  be  seen  at  c. 

Many  of  the  Crustacea  have  hairs  upon  their 
shells.  Those  upon  the  flabellum  of  the  common 
crab  have  minute  bristles  on  one  side  of  the  parent 
stalk,  so  as  to  form  a  little  comb,  with  which  to 
brush  off  the  impurities  from  its  branchiae.  This 
structure  is  seen  at  figure  191  in  plate  7.  A  live 
crab  from  the  aquarium  may  be  watched  for  the 
purpose  of  observing  these  cleanly  movements. 

The  study  of  the  uses  of  the  epidermal  ap- 
pendages is  one  full  of  interest,  as  in  no  one 
set  of  structures  do  we  find  a  greater  variety  of 
adaptations  of  a  common  plan  to  the  wants  of  the 
creatures  in  which  they  ,are  found.  The  feathers 
of  birds  belong  to  the  same  type  of  structure  as 
the  hairs  of  animals.  If  the  pinnae  of  a  common 
goose-quill,  used  for  a  pen,  are  examined,  the 
pinnules  will  be  found  to  be  covered  with  minute 
hooks,  drawn  in  figures  192  and  193,  plate  7.  These 
hooks  on  the  upper  surface  are  so  arranged  that  they 
catch  the  nearly  plain  and  slightly  toothed  pinnules 
on  the  lower  side. 

The  down  from  the  feathers  of  the  swan,  with 
which  pillows  and  beds  are  stuffed,  is  also  a  beau- 
tiful object,  and  its  microscopic  structure  will  at 
once  reveal  the  cause  of  its  lightness,  softness,  and 
warmth.  This  is  seen  at  figure  194,  in  the  7th 
plate. 

Amongst  the  creatures  which  domesticate  with 
G  2 


84  A    HALF    HOUR    WITH    THE 

us  are  certain  insects  which  are  more  frequentiv 
discovered  than  acknowledged.  However  dis- 
agreeable their  presence  may  be,  they  become 
interesting  objects  for  microscopic  investigations, 
and  are  not  less  calculated  to  excite  our  admira- 
tion than  creatures  more  ceremoniously  treated. 
"We  first  call  attention  to  the  common  flea  (Pulex 
irritans).  This  beautiful  insect  belongs  to  a  large 
family,  each  species  of  which  has  its  peculiar  habitat 
in  the  epidermal  appendages  of  some  of  the  higher 
animals.  The  head  of  the  human  flea  may  be  taken 
as  the  type  of  the  family.  This  is  represented  with 
great  accuracy  at  figure  19o,  in  plate  7.  It  is 
furnished  with  antennae,  mandibles,  and  a  pair  of 
lancet-shaped  jaws,  with  which  it  makes  little 
wounds  in  the  skin,  and  into  which  it  pours  the 
irritating  secretion  which  renders  its  bite  a  source 
of  annoyance.  Its  eye,  large  hind  legs,  and  orna- 
mental saddle  on  its  back,  are  all  deserving  of 
attention. 

Let  us  now  seek  another  too  common  inhabitant 
of  London  houses,  the  bed-bug  (Gimex  lectulwiua), 
and,  having  decapitated 'him,  submit  his  head  to  a 
low  power.  He,  too,  is  a  biting  creature  ;  and  you 
will  observe,  as  drawn  in  figure  19G,  that  his  jaws 
are  finer  than  those  of  the  flea,  and  are  like  a  pair 
of  excessively  fine  sharp  hairs  ;  they  are  inclosed  in 
a  sheath,  from  whence  they  are  projected  when 
used.  In  the  same  sheath  is  the  tongue,  which 
performs  the  double  office  of  depositing  in  the 
wound  an  acrid  and  irritating  secretion  and  suck- 
ing up  the  blood  of  its  victim.  The  antennae  and 
eyes  of  the  bug  are  also  worthy  of  examination. 
From  the  latter  will  be  found  projecting  minute 
hairs. 

A  still  more  despised  animal  may  now  be  sought 
(PedicuZus).  It  also  belongs  to  a  large  family,  and 


MICROSCOPE    1K-DOOBS.  85 

each  mammal  and  bird  seems  to  be  attended  with 
its  peculiar  louse.  Two  species  are  found  in  dirty 
and  diseased  conditions  of  the  human  body.  Dis- 
gusting as  connected  with  want  of  cleanliness,  they 
are,  nevertheless,  perfectly  harmless.  The  head  and 
mouth,  drawn  in  figure  198,  indicate  that  these 
creatures  are  adapted  to  live  on  the  secretions  of 
the  skin.  The  above  animals  all  belong  to  the 
much  larger  group  of  creatures  adapted  to  live  as 
parasites  upon  other  animals. 

The  head  of  the  common  gnat,  figured  at  199, 
in  plate  7,  may  be  now  examined  for  the  sake  of 
comparison.  In  this  creature,  the  eye  of  the  insect 
may  be  studied.  It  is  what  is  called  a  compound 
eye,  and  is  composed  of  innumerable  small  lenses ; 
each  one  of  which  is  connected  with  a  twig  of  the 
optic  nerve,  and  capable  of  receiving  impressions 
from  external  objects.  The  little  lenses  terminate 
on  the  convex  surface  of  the  eye,  presenting  an 
immense  number  of  hexagonal  facets.  These  are 
seen  at  figure  210,  plate  7.  In  the  common 
house-fly,  there  are  said  to  be  4,000  of  these  facets; 
and  in  the  cabbage-butterfly  17,000.  The  antennae 
of  the  gnat  are  very  beautiful ;  and,  in  fact,  these 
organs  in  insects  afford  an  endless  variety  of  forms. 
At  their  base,  in  the  gnat,  is  seen  a  round  process 
on  which  these  are  seated,  and  it  has  been  supposed 
that  they  are  organs  of  hearing.  Whether  they 
are  organs  of  hearing  or  not,  it  is  very  certain  that 
they  are  organs  of  touch,  and  the  creature  is  very 
susceptible  of  the  slightest  stimulus  applied  to 
them. 

The  head  of  the  honey-bee  may  be  now  examined ; 
and  if  a  careful  dissection  is  made  of  its  mouth,  a 
marvellous  apparatus  is  unfolded  to  view,  which  is 
exhibited  in  figure  201,  plate  7,  At  the  base  is 
seated  the  so-called  mentum,  and  on  each  side  aro 


86  A   HALF-HOUR   WITH   THE 

placed  the  mandibles  ;  above  these,  and  longer,  are 
the  maxillce,  and  on  each  side  of  the  prolonged 
central  organ,  called  the  tongue,  are  placed  the  labial 
palpi.  The  tongue  can  be  retracted  between  the 
palpi  as  into  a  sheath.  It  is  marked  by  a  series  of 
annular  divisions,  and,  by  a  high  power,  will  be 
seen  to  be  covered  over  with  hairs.  This  is  the 
organ  by  means  of  which  the  bee  "  gathers  honey 
all  the  day." 

Whilst  examining  the  bee,  its  sting  may  be 
taken  out  and  placed  under  a  low  power,  when  it 
will  be  found  to  present  the  appearance  of  a  pair 
of  spears  set  with  recurved  barbs,  which  run  part 
of  the  way  down  one  side  of  each  half  of  the  sting. 
This  is  seen  in  the  7th  plate,  figure  200.  Each  of 
these  spears  is  grooved  on  the  opposite  side,  the 
two,  when  united,  forming  a  canal,  down  which  are 
poured  the  contents  of  the  poison-bag,  producing 
the  painful  effects  of  wounds  from  these  instru- 
ments. 

To  return  to  the  head  and  mouth  of  insects  : — 
The  tongue  of  the  bee  may  now  be  compared  with 
the  same  organ  in  the  butterflies,  which  in  them 
assumes  the  form  of  a  proboscis,  and  is  called  the 
hausteHum,  seen  at  figure  203,  plate  7.  This 
instrument  is  coiled  up  when  the  insect  is  at  rest, 
and  is  the  organ  by  means  of  which  the  creature 
sucks  up  its  nutriment  from  the  flower.  It  has  a 
series  of  lines  running  across  it. 

If  the  head  of  the  common  blowfly  be  now 
examined,  it  will  be  seen  that  the  tongue,  instead 
of  being  elongated  as  in  the  latter  instances,  is 
expanded  laterally.  This  is  represented  in  figure 
202,  plate  7.  It  is  a  very  beautiful  object,  and 
when  viewed  by  transmitted  light,  a  series  of  spiral 
bands  are  observed  to  wind  across  each  half  of  the 
tongue. 


MICROSCOPE   IN-DOORS.  87 

The  head  of  the  common  garden  spider  (Eperia 
diadema)  presents  an  interesting  development  of 
the  mandibles.  These  organs  are  in  pairs ;  each 
mandible  consists  of  two  joints  :  one  is  small, 
sharp,  and  hooked ;  whilst  the  other  is  large  and 
short,  and  contains  within  it  a  bag,  or  poison- 
gland  ;  so  that  when  the  creature  seizes  its  prey, 
the  bag  is  pressed  on,  and  a  drop  of  the  poison 
exudes.  This  organ  is  represented  in  figure  204, 
plate  7.  This  structure  is  similar  to  what  is  met 
with  in  the  poisonous  serpents,  where  a  poison-bag 
is  seated  at  the  base  of  a  tubular  tooth. 

The  description  above  given  is  the  generally 
received  one ;  but  Mr.  John  Blackwall,  our  greatest 
authority  on  spiders,  considers  the  use  of  the  term 
"  mandibles  "  to  parts  entirely  without  the  mouth 
objectionable  ;  he  has  accordingly  bestowed  the 
name  of  "falees"  upon  them.  Some  carefully- 
conducted  and  interesting  experiments  of  his  on 
their  so-called  poisonous  secretion  seem  to  throw 
great  doubts  on  the  propriety  of  regarding  them  in 
this  light,  and  he  has  been  led  to  consider  that  the 
purposes  of  it  may  rather  be  to  deaden  pain  and 
still  the  struggles  of  a  captured  animal,  as  chloro- 
form is  given  previous  to  and  during  operations  on 
human  beings. 

The  head  of  the  spider  affords  also  a  good 
example  of  what  are  called  simple  eyes.  Besides 
the  compound  ones  before  mentioned,  insects  have 
also  these  simple  eyes — drawn  at  figure  208, 
plate  7.  They  consist  of  a  single  lens,  as  seen  at 
a,  and  are  placed  in  various  positions  in  the  heads 
of  spiders. 

The  skin  of  the  common  garden  spider  is  covered 
with  hairs.  These  appear  to  surmount  a  series  of 
concentric  plates,  seen  at  figure  209,  plate  7. 
They  vary  in  form  in.  different  species  of  spider ; 


88  A   HALF- HOUR   WITH   THE 

and  the  skin  of  all  should  be  examined  for  tlio 
purpose  of  observing  these  differences.  The  web 
of  the  spider  should  also  be  examined.  The  cords 
of  these  beautiful  structures,  which  run  from  the 
centre  to  the  circumference  of  the  web,  are  plain, 
as  seen  at  figure  214  ;  whilst  those  which  form 
the  concentric  lines  are  beaded  with  drops  of  a 
glutinous  substance.  It  is  by  means  of  this  adhe- 
sive matter  that  the  webs  are  held  together.  Nor 
should  the  rnicroscopist  neglect  examining  the 
spinnarets  of  the  spider,  by  which  these  beautiful 
threads  are  elaborated. 

The  breathing  organs  of  insects  are  well  de- 
serving attention.  Their  bodies  are  perforated  at 
the  sides,  and  the  openings  thus  formed,  called 
apirades,  lead  into  tubes  which  are  branched,  and 
are  called  trachece.  These  air-tubes  are  composed 
of  a  delicate  membrane,  which  is  supported  on  a 
series  of  delicate  rings,  which  are  easily  traced  into 
the  more  minute  branches.  They  are  well  seen  in 
the  larvse  of  most  of  the  lepidopterous  insects,  and 
represented  from  a  caterpillar  in  figure  222, 
plate  8.  The  spiracle  is  not  an  open  hole.  In  the 
common  house-fly,  seen  at  figure  212,  plate  7,  and 
the  water-beetle  (Dyticus],  in  figure  213,  it  is 
covered  over  with  irregular  branched  processes 
from  the  sides  of  the  opening.  The  object  of  this 
obstruction  is  probably  to  prevent  particles  of  dust, 
and  other  foreign  substances,  from  entering  the  air- 
passages,  and  thus  choking  the  animal. 

The  legs  of  insects  \vill  afford  an  almost  un- 
limited supply  of  objects  for  examination.  The 
spoilt  specimens  of  a  summer's  capture  may  well 
supply  materials  for  a  winter's  examination.  The 
legs  of  insects  are  composed  generally  of  five  parts, 
jointed  together.  The  lowest  of  these  is  called  the 
tarsus,  or  foot.  It  is  variously  formed  to  adapt  it 


m 

London :  "Robert  Eardwi&kB,  i860-. 


MICROSCOPE    IK-DOORS.  89 

to  the  locomotive  habits  of  the  insect.  In  the 
common  fly  it  is  terminated  with  a  pair  of  disks, 
which  are  covered  with  suckers,  called  pulvilli. 
Those  of  the  Empis,  a  species  of  fly,  are  drawn  at 
figure  205,  plate  7.  By  means  of  these  suckers  the 
animal  is  enabled  to  lay  hold  of  smooth  surfaces,  and 
thus  to  crawl  up  them.  They  also  exude  a  glutinous 
matter,  which  assists  in  this  process.  The  same 
kind  of  arrangement  is  observed  in  the  common 
bee,  represented  in  figure  20G.  The  feet  are  also 
covered  with  hairs,  and  are  frequently  suppMcd  with 
hooked  joints,  which  assist  the  animals  in  laying 
hold  of  rough  objects  where  their  suckers  would  be 
of  no  use.  In  the  spicier  there  are  no  suckers,  but 
the  hooked  joints  and  hairs  enable  the  creature  to 
crawl  with  facility.  These  hooks  are  seen  in  the 
foot  of  the  spider  in  figure  207,  plate  7.  In  the 
Dyticus  the  fore  leg  is  supplied  with  two  large 
suckers,  which  are  seen  in  figure  218,  plate  8, 
besides  a  number  of  smaller  ones,  and  a  hook  ; 
whilst  the  foot  of  the  middle  leg  is  destitute  of  the 
largo  suckers,  as  seen  at  figure  219. 

The  legs  of  beetles  are  often  covered  with  little 
cushion-like  bodies,  which  undoubtedly  act  as 
suckers.  These  are  seen  at  figures  215,  216,  217. 
The  three  legs  often  differ  very  much  from  each  other, 
and  probably  perform  modified  functions,  according 
to  their  structure.  This  is  well  seen  in  the  legs  of 
the  whirligig-beetle  (Gyrinus  natator\  in  which  the 
first  leg,  in  figure  215,  is  very  much  elongated, 
whilst  the  third  is  broad  and  short,  as  at  figure  217. 
and  adapted  for  swimming,  from  its  oar-like  form. 
The  second  leg,  seen  at  figure  216,  is  intermediate 
in  form  and  size. 

As  a  contrast  to  these  legs,  adapted  for  the 
varied  functions  of  the  perfect  insect,  the  leg  of 
any  common  caterpillar  may  be  examined  ;  when  it 


90  A   HALF- HOUR    WITH   THE 

will  be  found  to  consist,  at  its  extremity,  of  a  little 
sac  surmounted  with  hooks.  These  hooks  are 
represented  in  figure  223,  plate  8. 

The  wings  of  insects,  too,  are  beautiful  objects  \ 
easily  investigated  by  a  low  power.  The  nerves 
which  run  through  them  are  supplied  with  tracheae, 
and  they  thus  become  organs  of  respiration.  The 
under  wing  of  the  bee  is  supplied  with  a  series  of 
hooks,  seen  at  figure  211,  plate  7,  which  slide  on 
a  thickened  nerve  on  the  upper  wing,  marked  a, 
and  keep  the  wings  steady  during  flight. 

The  lepidopterous  insects,  including  the  butter- 
flies and  moths,  have  got  their  name  from  the  scales 
on  their  wings.  These  scales  assume  a  wonderful 
variety  of  form,  and  claim  a  large  amount  of  atten- 
tion from  the  microscopic  observer,  and  cannot  be 
neglected  by  the  entomologist. 

The  little  blue  argus  butterfly  has  scales  in  the 
shape  of  a  battledore,  drawn  at  figure  225,  plate  8, 
the  handle  being  the  part  attached  to  the  wing. 
All  the  scales  have  handles  of  this  sort,  whatever 
be  their  shape.  At  figure  226,  a  scale  of  ordinary 
shape  is  represented.  Sometimes  the  scale  is  broad 
at  the  base,  and  pointed  at  top.  In  the  meadow- 
brown  butterfly,  the  point  is  surmounted  with  little 
clubbed  projections,  drawn  at  figure  227.  Scales 
are  found  on  other  insects  besides  moths  and  butter- 
flies :  thus  they  are  found  on  the  common  gnat. 
These  are  shown  at  figure  228.  Besides  their 
curious  forms,  the  scales  are  marked  with  lines 
which  are  exceedingly  delicate,  and  require  the 
highest  powers  of  the  Microscope  to  bring  them 
out.  Some  of  the  scales  are  thus  used  as  tests  for 
the  powers  of  the  Microscope. 

Just  as  we  have  seen  in  the  tongues  and  legs  of 
insects,  the  same  parts  expanded  or  compressed 
according  to  the  wants  of  the  animal,  so  we  find  the 


MICROSCOPE   IN-DOORS.  91 

scales  assuming  various  forms.  The  scales  stand  in 
exactly  the  same  relation  to  the  hairs  in  insects, 
that  the  scales  of  fishes  and  reptiles  do  to  the 
feathers  of  birds  and  the  hairs  of  mammals.  Hair- 
like  scales  are  therefore  not  uncommon.  At  figures 
229  and  230,  such  scales  are  represented,  and  may 
be  found  on  the  common  clothes-moth. 

The  young  microscopist,  for  whom  our  book  is 
written,  and  with  which  we  hope  to  make  him 
dissatisfied,  in  order  to  facilitate  his  progress  in 
natural  history  inquiries,  will  not  spend  much  time 
in  making  dissections.  Should  he  wish  to  do  so,  he 
well  find  the  structure  of  insects  full  of  interest. 
He  has  only  to  open  a  cockroach  to  see  how 
curiously  their  digestive  apparatus  is  constructed. 
This  insect  has  a  gizzard,  and  at  the  upper  part  it 
is  beset  with  six  conical  teeth,  as  seen  at  #,  in 
figure  220,  plate  8;  these  teeth,  working  together, 
reduce  its  food  to  a  pultaceous  mass  previous  to 
digestion.  When  cut  open,  their  position  and  re- 
lations can  be  easily  seen,  as  figured  at  b.  The 
gizzard  of  the  cricket  is  also  supplied  with  teeth, 
seen  at  a,  figure  221  ;  it  has  three  longitudinal 
series  of  teeth,  and  each  row  in  each  series  contains 
seven  teeth.  The  family  of  insects  to  which  the 
cricket  belongs  (Orthopt&ra)  affords  several  other 
instances  of  the  same  kind  of  structure  in  the 
gizzard.  It  will  be  interesting  to  compare  these 
teeth  of  the  insects  with  those  of  the  mollusca  and 
the  wheel  animalcules. 

We  must  satisfy  ourselves  with  having  shown 
the  student  the  way  to  cultivate  a  large  field  of 
interesting  and  instructive  phenomena  in  the  insect 
world,  without  going  further  into  detail. 

The  tissues  or  textures  of  which  animals  are 
built  up  or  made  may  be  easily  procured  in-doors. 
We  have  spoken  of  the  hard  parts  which  form  the 


02  A    HALF-HOUR   WITH    THE 

outer  skeleton  of  the  lower  animals,  as  the  mol- 
luscs, crabs,  and  fishes  ;  the  internal  skeleton  of 
the  higher  animals  affords  a  not  less  interesting 
field  of  research.  If  we  take  a  piece  of  bone,  and 
having  ground  it  so  fine  that  we  may  examine  it 
with  transmitted  light  under  the  Microscope,  we 
shall  find  it  composed  of  a  number  of  minute 
insect-shaped  cells,  surrounding  an  open  canal,  as 
seen  at  figure  232,  plate  8.  These  cells,  which  are 
called  lacunas,  and  their  little  branches  canaliculi, 
are  modifications,  of  the  cells  found  in  fishes'  scales, 
and  figured  at  175,  plate  6. 

These  curiously-shaped  cells  differ  in  size  and 
form  in  the  various  classes  of  animals  belonging  to 
the  sub-kingdom  Vertebrata,  and  thus  a  small  por- 
tion of  a  bone  will  frequently  serve  to  indicate 
whether  an  animal  belonged  to  fishes,  reptiles,  birds, 
or  mammals.  This  is  a  matter  of  importance  to 
the  geologist  in  determining  the  character  of  the 
inhabitants  of  the  earth  at  former  periods  of  its 
history.  A  section  of  whalebone  is  figured  at  242, 
plate  8. 

The  shells  of  eggs  seems  to  be  formed  on  the 
same  general  principles  as  other  hard  parts,  and  the 
tendency  to  the  formation  of  cells  with  canaliculi 
may  be  easily  observed,  as  in  the  section  of  a  com- 
mon egg-shell,  represented  at  figure  181,  plate  6. 
The  young  egg-shell  should  be  examined,  a  section 
of  which  is  seen  at  182,  if  the  object  is  to  study  the 
history  of  the  development  of  the  shell ;  and  this 
may  be  compared  on  the  one  hand  with  the  shells 
of  the  Mollusca  and  the  Crustacea,,  and  on  the  other 
hand  with  those  of  the  scales,  teeth,  and  bones  of 
the  vertebrate  animals.  Egg-shells  present  very 
different  appearances.  The  shell  of  the  emu,  for 
instance,  exhibits  a  series  of  dark  triangular  spots, 
and  is  represented  at  figure  183,  plate  6. 


MICROSCOPE   IN-DOORS.  03 

As  one  of  the  hard  parts  of  animals,  the  struc- 
ture of  cartilage  is  very  interesting.  A  slice  may 
be  obtained  from  the  gristle  of  any  young  animal 
Its  structure  is  best  seen  in  the  mouse's  ear,  repre- 
sented at  figure  231,  plate  8.  No  one  who  looks 
at  this  object  can  but  be  struck  with  its  resemblance 
to  vegetable  tissue ;  and  it  was  this  resemblance 
which  led  to  the  application  of  the  cell  theory  of 
development,  which  had  been  made  out  in  vegetable 
structures,  to  those  of  animals. 

Many  of  the  soft  parts  of  animal  tissues  afford 
instructive  objects  under  the  Microscope.  If  the 
tongue  is  scraped,  and  a  drop  of  the  saliva  thus 
procured  placed  under  the  Microscope,  it  will  be 
found  to  contain  many  flat,  irregular,  scale-like 
bodies  with  a  nucleus  in  the  centre,  such  as  are  seen 
at  figure  4,  plate  1.  These  scales  are  flattened  cells, 
and  closely  resemble  those  found  on  the  surface  of 
the  skin.  Cells  of  a  different  kind  line  the  air- 
passages.  If  a  snip  be  taken  from  inside  the 
nostril  of  a  recently  killed  ox  or  sheep,  it  will  be 
found  to  be  composed  of  cells  which  are  fringed 
with  cilia  at  the  top.  These  are  seen  at  Figure  5, 
Plate  1.  These  cilia  are  constantly  moving,  and 
produce  the  motion  of  the  mucus  on  the  surface  of 
these  passages  which  is  essential  to  their  healthy 
action. 

The  blood  of  animals  presents  us  with  objects  of 
high  interest.  The  human  blood  consists  of  a  liquid 
in  which  float  two  kinds  of  cells.  They  are  discoid 
bodies,  from  the  three- thousandth  to  the  three- 
thousand-five -hundredth  of  an  inch  in  diameter 
(___!__  to  3-¥Vo)?  and  about  a  fourth  of  that  size  in 
thickness.  They  are  represented  at  figure  6, 
plate  1.  They  are  of  two  sorts — pale  and  red  ;  the 
latter  are  rather  smaller,  but  are  by  far  the  most 
abundant.  They  present  a  little  spot  in  the  centre, 


34  A    HALF-HOUR   WITH   THE 

which  is  called  a  nucleus,  and  this  again  another 
little  spot,  which  is  called  a  nudeolus.  The  red 
globules  vary  much  in  size  and  form  in  different 
animals.-  Thus,  in  birds,  reptiles,  and  fishes,  they 
are  oval  instead  of  round  ;  and,  mostly,  in  these 
three  classes  much  larger  than  in  mammals.  This 
is  especially  the  case  in  the  batrachian  reptiles,  to 
which  the  frog  -and  toad  belong.  Those  from  the 
frog  are  shown  at  figure  8,  plate  1.  In  the  fowl, 
shown  at  figure  7,  and  in  the  sole,  seen  at  figure  9, 
they  are  nearly  twice  as  large  as  in  man.  In  the 
insects  they  are  also  frequently  of  large  size,  as  in 
the  cockchafer,  seen  at  figure  10. 

The  proof  that  blood-stains  have  been  produced 
by  human  blood  on  articles  of  dress  and  other 
things,  is  frequently  important  in  medico-legal  in- 
vestigations. Although  it  cannot  be  distinguished 
from  all  other  kinds  of  blood,  it  may  be  from  some  ; 
and  the  Microscope  has  been  employed  as  an  adjunct 
in  such  cases. 

The  structure  of  the  skin,  and  other  organs  of 
the  body,  are  very  interesting  subjects  for  micro- 
scopical investigation  ;  and  volumes  have  been 
written  upon  their  diversified  details.  The  struc- 
ture of  voluntary  and  involuntary  muscular  tissue 
may  be  easily  examined,  especially  the  former,  by 
taking  a  portion  of  the  flesh  of  any  animal  usually 
eaten  as  food.  The  striated  fibrillae  of  voluntary 
muscle  may  be  best  seen  in  flesh  cooked  as  food. 
A  muscle  consists  of  bundles  of  fibres,  and  each  of 
these  fibres  consists  of  several  fibrillse  lying  close 
together.  Each  of  these  fibrils  is  seen  to  be  crossed 
with  lines,  represented  in  figure  233,  plate  8. 
These  lines  indicate  the  point  of  union  of  the 
string  of  cells  which  form  the  ultimate  parts  of  the 
muscular  tissue. 

The  structure  of  nervous  tissue  is  also  one  of 


MICROSCOPE   1N-DOORS.  95 

high  interest  to  the  physiologist,  bub  it  requires 
the  highest  powers  of  the  Microscope,  and  great 
skill  in  manipulation,  to  make  out. 


96  A    HALF-HOUR    WITH 


CHAPTER    VII. 
A  HALF-HOUR  WITH  POLARIZED  LIGHT. 

WHAT  is  polarized  light,  and  in  what  does  it 
differ  from  ordinary  light  1  This  question  is  often 
asked,  and,  like  many  other  questions  in  physical 
and  natural  science,  more  easily  asked  than  an- 
swered. 

To  enable  the  young  microscopist  to  form  some 
conception  of  the  difference  between  common  or 
ordinary  light  and  that  known  as  polarized  light, 
it  will  be  necessary  to  form  some  definite  idea  of 
light  itself. 

Light,  according  to  the  modern  theory,  is  pro- 
duced by  the  vibrations  or  undulations  of  an  ima- 
ginary fluid  called  ether  ;  this  is  supposed  to  be  a 
rare  and  highly  elastic  fluid,  occupying  all  space 
and  pervading  all  bodies  :  the  vibrations  of  this 
medium  produce  light,  just  as  the  vibrations  of 
air  produce  sound. 

The  length  of  these  vibrations  is  inconceivably 
minute,  and  their  rapidity  is  represented  by  num- 
bers which  the  human  mind  can  scarcely  compre- 
hend. Upon  the  relative  lengths  of  these  vibra- 
tions depend  the  differences  of  colour,  red  being 
produced  by  the  longest,  and  violet  by  the  shortest 
waves  or  vibrations. 

For  the  production  of  the  red  ray,  37,640,  and 
for  the  violet  ray  59,750  undulations  in  an  inch 
are  requisite.  In  the  production  of  the  red  ray 
458  millions  of  millions,  and  in  the  violet  ray 
727  millions  of  millions  of  undulations  take  place 


POLARIZED    LIGHT.  97 

in.  a  second  of  time.  White  light  is  produced 
when  the  undulations  are  44,440  in  an  inch,  and 
their  number  in  a  second  of  time  amounts  to  541 
millions  of  millions.  These  vibrations  are  com- 
municated to  the  retina  and  optic  nerve,  and  from 
thence  to  the  brain.  The  rapidity  with  which 
these  undulations  are  communicated  from  their 
source  to  the  eye  may  be  imagined  when  it  is 
stated  that  the  light  from  the  sun  (a  distance  of 
about  90  millions  of  miles)  reaches  us  in  8  minutes 
and  13  seconds;  a  railway  train  travelling  at  the 
speed  of  60  miles  an  hour  would  require  180  years 
to  accomplish  the  same  distance.  The  light  from 
remotest  nebula  (according  to  Sir  W.  Herschel) 
would,  however,  require  2,000,000  years  to  reach 
the  earth. 

A  ray  of  common  light  is  supposed  to  have  at 
least  two  sets  of  vibrations ;  viz.,  one  vertical  (or 
up  and  down),  and  the  other  horizontal  (or  from 
side  to  side). 

These  vibrations  aro  capable  of  being  separated 
either  by  reflection  or  by  passing  the  ray  through 
certain  transparent  substances.  The  light  is  then 
said  to  be  polarized.  The  name  is  not,  perhaps, 
the  best  that  could  have  been  chosen,  but  as  it 
has  been  in  use  for  many  years,  any  alteration 
would  be  attended  with  inconvenience. 

The  terms  poles  and  polarity  are  usually  em- 
ployed to  describe  the  contrary  properties  pos- 
sessed by  the  opposite  ends  of  bodies.  Thus,  we 
have  the  north  and  south  poles  of  a  magnet,  one 
of  which  attracts  what  the  other  repels  \  and  when 
it  was  found  that  the  sides  of  a  beam  of  light, 
when  reflected  or  transmitted  under  certain  con- 
ditions, possessed  opposite  properties,  the  ray 
was  said  to  be  polarized  from  a  fancied  resem- 
blance to  the  poles  of  a  magnet  or  galvanic  battery, 
it 


A   HALF-HOUR   WITH 


An  imaginary  section  of  a  beam 
of  common  light  is  usually  repre- 
sented thus  : and,  of  a  beam 

of  polarized  light . 

In  the  following  or 

diagrams  we  shall  represent  the  ordinary  beam 
by    three,    the    ordinary     polarized    ray    by   two 
parallel  lines,  and  the  extraordinary  polarized  ray 
by  a  single  line. 


If  a  ray  of  light  (Fig.  16)  b  impinges  on  a  bundle 
of  glass  plates,  a,  placed  at  the  polarizing  angle  of 
glass  (56°  45')  the  ray  is  in  part  reflected  and  in 
part  transmitted,  and  both  become  polarized  j  c  is 
termed  the  ordinary,  and  d  the  extraordinary  ray. 


Fig.  16. 

a,  bundle  of  plates  of  thin  glass  ;  5,  ray  of  ordinary  light ; 
<;,  ray  polarized  by  reflection ;  d,  ray  polarized  by  refraction. 


A  polarized  ray  may  be  obtained  by  reflection 


POLARIZED    LIGHT.  99 

from  most  polished  surfaces,  such  as  a  mahogany 
table,  a  tea-tray,  a  piece  of  japanned  leather,  &c. 

During  the  earlier  and  later  periods  of  the  day, 
the  light  reflected  from  that  portion  of  the  sky 
opposite  the  sun  is  always  polarized. 

It  will  thus  be  seen  that  polarized  light  is  of 
common  occurrence,  but  the  unassisted  eye  is  un- 
able to  detect  it,  although  one-half  of  the  ordinary 
beam  is  lost.  "We  may  here  remark  that  the  loss 
of  light  caused  by  various  optical  contrivances  is 
not  usually  detected  by  the  eye.  This  is  well 
illustrated  by  the  Binocular  Microscope.  Let  an 
object  be  examined  with  the  tube  directly  over 
the  prism  with  the  prism  in  position ;  if  we  re- 
move the  eye  for  an  instant,  and  withdraw  the 
prism,  no  difference  will  be  detected,  although  in 
the  latter  case  double  the  amount  of  light  has 
been  transmitted  through  the  tube. 

This  non-appreciation  of  an  increase  or  diminu- 
tion of  light  to  the  extent  of  50  per  cent,  is  per- 
haps owing  to  the  dilation  and  contraction  of  the 
pupil  of  the  eye. 

If  the  reflected  and  refracted  beams  of  polar- 
ized light  are  thrown  simultaneously  on  a  white 
ceiling  and  a  white  screen,  the  spectator  will 
observe  two  spots  of  light  of  equal  intensity. 
A  polarized  ray  may  be  obtained — 

1.  By  reflection. 

2.  „    simple  refraction. 

3.  „    double  refraction. 

4.  „    transmission  through  a  plate  of  tour 

maline  or  crystal  of  herapathite. 

The  diagram  (fig.  16)  on  page  98  represents 
the  two  first,  c  being  the  reflected,  and  d  the 
refracted  ray. 

The  polarization  of  a  ray  of  ordinary  light  by 
H  2 


100 


A   HALF-HOUR   WITH 


double  refraction  is  shown  in  fig.  17 ;  a  is  a  rhom- 
boidal  crystal  of  Iceland  spar.     These  crystals  have 


Fig.  17. 

a,  rhomb  of  Iceland  spar  ;  b,  ray  of  common  light ;  c,  or- 
dinary ray  of  polarized  light ;  d,  extraordinary  ray  of 
polarized  light. 

the  property  of  splitting  the  impinging  ray  into  two ; 
thus,  if  a  small  hole  is  made  in  a  card,  and  viewed 
through  a  rhomb  of  Iceland  spar,  two  discs  of  light 
will  be  seen  ;  or,  if  a  black  line  is  drawn  on  a 
piece  of  paper,  two  images  of  it  will  appear. 

b  is  the  ray  of  common  light  which  becomes 
divided  as  it  passes  through  the  crystal.  These 
rays  are  both  polarized. 

Certain  varieties  of  tourmaline,  when  cut  into 
plates  parallel  to  the  axis  of  the  crystal,  possess 
the  property  of  polarizing  common  light.  Fig.  18 
represents  such  a  plate. 

Having  seen  how  a  polarized  ray  can  be  ob- 
tained, the  reader  will  ask,  How  am  I  to  recognize 
this  condition  of  light ;  fur  you  have  already  told 


POLARIZED    LIGHT. 


101 


me  that  it  is  not  to  be  detected  bv  the  unassisted 
eye] 


Fig.,  18. 

a,  plate  of  tourmaline  ;  &,  ray  of  common  light ;    c,  ray  of 
polarized  light. 

In  order  to  distinguish  the  difference  between 
ordinary  light  and  that  which  has  become  polar- 
ized, special  means  are  required  for  that  purpose. 
It  is  an  axiom  that  the  medium  capable  of  pro- 
ducing polarized  light  is  also  capable  of  analyzing 
it.  Thus,  if  the  reflected  ray  c  (Fig.  16,  page  9G) 
is  reflected  on  a  mirror  whose  surface  coincides 
with  that  of  the  polarizer,  the  ray  will  be  reflected 
in  the  same  manner  as  an  ordinary  ray  j  but  if  we 
gradually  revolve  it  until  it  stands  at  right  angles 


CL 


of 


d 


Fig.  19. 

a  a,  two  slices  of  tourmaline  -with  angles  coincident ; 
I,  beam  of  common  light ;  c,  polarized  ray  ;  d,  ditto  trans- 
mitted. 

to   the  polarized,  the  ray  is  intercepted  and  de- 
stroyed. 


102 


A    HALF-HOUR    WITH 


Let  a  a'  represent  two  plates  of  tourmaline 
with  their  angles  coincident,  a  is  the  polarizer  and 
of  the  analyzer ;  with  the  plates  in  this  position, 
the  polarized  ray  c  passes  through  to  d  (Fig.  19). 


Fig.  20. 

6  &',  two  slices  of  tourmaline  crossed ;  6,  beam  of  common 
light ;  c,  polarized  ray  stopped  by  &'. 

If  we  now  cross  the  plates,  the  ray  c  is  no  longer 
transmitted.  If  the  analyzer  is  now  revolved 
another  90°,  the  ray  is  again  transmitted.  Re- 
volve it  90°  more,  the  ray  is  stopped ;  and,  on  the 
completion  of  the  circle,  the  ray  again  becomes 
visible. 

The  following  diagram  illustrates  the  effect  of 


the  various  positions  of  the  analyzer.     At  a  the 
ray  is  visible,  at  6  invisible,  at  c  visible,  at  d  in- 


POLARIZED    LIGHT. 


103 


visible ;  as  the  analyzer  passes  from  a  to  6,  the 
brightness  of  the  image  gradually  diminishes ;  from 
6  to  c  the  brightness  increases.  The  positions 
marked  1,  2,  3,  4,  are  called  the  neutral  axes,  only 
half  the  amount  of  light  being  transmitted. 

In  order  to  analyze  a  polarized  beam  it  is  not 
necessary  that  the  analyzer  should  be  of  the  same 
material  as  the  polarizer  ;  a  reflected  ray  may  be 
examined  by  a  tourmaline  or  crystal  of  Iceland 
spar,  and  a  refracted  or  transmitted  ray  can  be 
reflected  from  the  surface  of  a  mirror. 

The  student  will  have  gathered  from  what  wo 
have  stated  in  the  preceding  pages,  that  the  effect 
of  an  analyzer  on  a  polarized  ray  is  the  alternate 
transmission  and  stoppage  of  that  ray.  The  most 
gorgeous  effects  are,  however,  obtained  when  a 
doubly  refracting  film  is  interposed  between  the 
polarized  ray  and  the  analyzer,  producing  what  is 
termed  "  chromatic  polarization." 

This  doubly  refracting  film  receives  the  polar- 
ized ray,  and  doubly  refracts  it ;  in  other  words, 
the  series  of  undulations  of  which  the  ray  is  com- 
posed on  entering  the  film  (sometimes  called  the 
depolarizer)  is  broken  into  two  systems  within  it, 
forming  the  ordinary  and  extraordinary  rays. 


Fig.  22. 

If  a  polarized  ray  is  allowed  to  enter  a  film  of 
selenite,  it  becomes  refracted,  and  forms  two  dis- 


104 


A    HALF-HOUR    WITH 


tinct  rays,  a  is  a  polarized  ray,  b  the  film  of 
selenite,  "  c  is  the  extraordinary  ray,  d  the  ordi- 
nary ray;  but  one  of  these  rays  is  retarded.  If 
they  are  analyzed  by  a  double-image  prism,  the 
ordinary  and  extraordinary  rays  will  again  bo 
divided  into  c  d,  c  c  and  d  d,  d  c ;  and  if  the 
original  ray  be  passed  through  a  circular  aperture, 
two  coloured  discs  will  be  observed,  the  colour 
depending  upon  the  thickness  of  the  selenite  film.  If 
one  disc  is  red,  the  other  will  be  green,  the  colours 
being  complementary  to  each  other. 

When  a  plate  of  tourmaline  or  a  Nichol's  prism 
is  used,  one  of  these  rays  is  alternately  suppressed. 
If  the  analyzer  is  revolved,  we  shall  find  that 
when  the  angles  of  the  polarizer  and  analyzer 
coincide,  and  supposing  a  red  and  green  selenite  is 
used,  the  colours  will  appear  in  the  following 
order  : — 


Fig.  23. 

At  a  the  ray  would  be  green,  at  b  red,  at  c 
green,  at  d  red  ;  as  the  analyzer  approached  1,  the 
colour  fades ;  when  it  reaches  that  position  the 
colour  will  disappear ;  as  it  approaches  5,  the  red 
increases  in  brilliancy  until  it  reaches  b,  when  it 
will  have  reached  its  maximum  brightness.  In 
the  positions  2,  3,  and  4,  no  colour  will  be  found. 


POLARIZED    LIGHT.  105 

Having  endeavoured  to  describe  as  plainly  as 
possible  the  nature  of  polarized  light,  we  will  now 
proceed  to  describe  the  methods  usually  adopted 
for  the  purpose  of  applying  polarized  light  to  the 
examination  of  microscopic  objects. 

The  micro-polariscope  usually  consists  of  two 
Nichol's  prisms,  mounted  in  appropriate  fittings. 
A  Nichol's  prism  is  composed  of  a  crystal  of  Ice- 
land spar.  It  will  be  remembered  that  a  beam 
of  light,  in  passing  through  a  rhomb  of  Iceland 
spar,  becomes  doubly  refracted,  and  both  polarized 
beams  are  visible  ;  for  polarizing  purposes  this  is 
not  by  any  means  desirable,  but  the  difficulty  lias 
been  overcome  in  the  following  manner.  A 
rhomb  is  divided,  as  shown  in  fig.  24,  and  the  two 
halves  cemented  with  Canada  balsam ;  the  re- 
fractive power  of  the  film  of  balsam  being  different 
to  that  of  the  spar,  throws  the  second  image  out 
of  the  field. 


Fig.  24. 

a,  section  of  Nichol's  prism  ;  &,  film  of  balsam  ;  c,  ray  of 
light;  d,  ditto  passing  out  parallel  to  that  of  incident  ray  ; 
€,  refracted  ray. 

a  represents  a  section  of  a  Nichol's  prism,  b  the 
cementing  film  of  Canada  balsam,  c  a  ray  passing 
into  the  prism,  d  the  same  passing  out  parallel 
to  the  incident  ray,  e  the  refracted  ray. 

One  of  these  prisms  is  mounted,  as  shown  in 
fig.  25,  and  is  made  to  slide  in  the  short  tube 
attached  to  the  under  side  of  the  stage ;  a  is  a 


10G 


A    HALF-HOUR    WITH 


revolving    collar  connected  with    the    tube    into 
which   tho  prism  is  fitted.      By  this  contrivance 


Fig.  25. 

the    surface    of  the    prism  can  be  placed  at  any 
angle  with  the  analyzer. 

The  prism  used  as  the  analyzer  is  sometimes 
mounted  in  a  brass  cap,  fitted  over  the  eye-piece, 
as  in  fig.  26  j  or  in  an  adapter  screwed  on  to  the 


Fig.  26. 

nose-piece  of  the  Microscope  into  which  the  object- 
glass  is  screwed. 

By  the  first  method  the  brightness  of  the  field 
and  the  definition  of  the  object  under  examination 
is  not  impaired,  but  the  diameter  of  the  field  is 
seriously  diminished.  By  the  latter  plan  the  field 
remains  the  same  size,  but  a  certain  amount  of 


POLARIZED    LIGHT. 


107 


definition  is  sacrificed  (this,  however,  is  scarcely 
perceptible  if  the  prism  is  of  good  quality). 
Having  fixed  the  polarizing  apparatus  to  the  Micro- 
scope, we  may  now  proceed  to  test  its  effects  on 
various  objects.  Some  will  be  tinted  with  all  the 
colours  of  the  spectrum,  whilst  others  are  either 
not  affected  by  the  altered  condition  of  the  light, 
or  are  merely  black  on  a  white  ground,  or  white 
on  a  black  ground.  The  last-named  objects  are 
best  seen  with  a  film  of  selenite  placed  beneath. 
This  is  sometimes  mounted  between  two  ordinary 
glass  slides  and  placed  below  the  object.  The 
selenite  should,  however,  be  mounted  in  such  a 
way  that  it  can  be  revolved  independently  of  the 
object.  This  is  done  in  several  ways;  the  best 
contrivance  is  perhaps  the  revolving  selenite  stage. 
The  following  diagram  represents  one  of  the 
simplest  forms  of  revolving  stage. 


Fig.  27. 

With  these  stages  a  set  of  selenites  is  usually 
supplied ;  these  separately  give  the  blue,  purple, 
and  red,  with  their  respective  complementaries 
orange,  yellow,  and  green. 

These  discs  generally  have  engraved  upon 
them  the  amount  of  the  retardation  of  the 


108  A    HALF-HOUR   WITH 

undulations  of  white  light  thus — J,  f ,  and  -f- ; 
and  if  these  are  placed  so  that  their  positive 
axes  (marked  P  A)  coincide,  they  give  the  sum  of 


Fig.  28. 

their  combined  retardations.  If  any  be  turned 
until  its  P  A  is  at  90°  to  the  P  A  of  the  othei-s, 
the  lesser  number  is  subtracted  from  the  greater. 
For  instance,  when  the  P  A  of  the  f  is  placed  at 
-right  angles  to  the  P  A  of  the  -£  the  sum  of  the 
difference  is  obtained  =  f;  if  the  -J  is  now  added 
with  its  P  A  coinciding  with  the  P  A  of  the  -»-,  % 
are  obtained  ;  but  if  placed  to  coincide  with  the 
P  A  of  the  f ,  |  is  the  result. 

Therefore  by  subtracting  by  90°,  or  adding  by 
the  P  A,  any  number  from  J  to  L3,  undulations 
may  be  retarded  which  includes  all  the  colours  of 
the  spectrum. 

To  those  who  may  wish  to  try  the  effect  of 
polarized  light  at  a  small  cost,  the  following  plan, 
suggested  by  Professor  Reinicke*  will  be  found 
useful. 

Procure  from  twenty  to  twenty-five  pieces  of 
thin  covering  glass  flat  and  free  from  veins.  The 
size  most  convenient  for  the  purpose  is  18x12 
mm.  Fig.  29  represents  the  exact  size.  These  are 
to  be  fixed  on  a  tube  at  an  angle  to  the  tube  of 


*  Tfie  Professor  gays  50  to  60,  but  with  that  number  the 
loss  of  light  is  considerable. 


POLARIZED    LIGHT. 


109- 


35°  25".     This  tube  may  be  made  of  cardboard,  as 
shown,  in  Fig.  30  (also  the  exact  dimensions).     The 


Fig,  29. 

width  from  a  to  I,  and  c  to  d  =  12mm.,  that  from 
b  to  c,  and  d  to  e,  equal  to  the  length  of  the  thin 
gliLss,  when  placed  at  the  proper  angle.  It  will  be 
found  convenient  to  cut  the  cardboard  partially 


9 

Firj.  30. 


through  with  a  sharp  knife  from  6  to/,  c  to  g,  and 
d  to  h ;  near  the  bottom  of  the  first  division  on 
the  other  side  paste  a  strip  of  card  i ;  carefully 
paste  the  two  edges  of  the  card  together;  drop 


110  A   HALF-HOUR   WITH 

the  pieces  of  glass  into  the  tube,  taking  care  that 
the  lower  edge  of  the  first  piece  rests  on  the  card- 
board lodge  L  When  all  the  pieces  are  in  posi- 
tion a  similar  strip  of  card  must  be  pasted  on  the 
upper  part  of  the  opposite  side  of  the  tube.  The 
analyzer  can  of  course  be  constructed  the  same 
way.  These  square  tubes  can  be  fitted  into  cylin- 
drical ones,  and  adapted  to  the  fittings  of  the 
Microscope. 

Although  with  this  form  of  polariscope  the 
young  student  will  be  able  to  examine  many 
objects  by  polarized  light,  the  Nichol  prisms  are 
far  superior  for  the  purpose,  and  most  of  the 
opticians  supply  the  polarizing  apparatus  for  stu- 
dents' Microscopes  at  a  moderate  cost  (from  30s. 
to  35s.). 

Having  now  described  the  Micro-polariscope, 
and  the  mode  of  using  it,  we  will  proceed  to  de- 
scribe a  few  of  those  objects  to  which  polarized 
light  may  be  effectively  applied.  Matter  pos- 
sessing a  crystalline  structure  as  a  rule  affords 
the  greatest  variety  of  form  and  colour.  The 
following  list  of  salts,  &c.,  most  of  which  are 
easily  procured,  give  a  brilliant  display  of  colour 
when  polarized  : — 

Chloride  of  Barium.* 
Chlorate  of  Potash.* 
Sulphate  of  Copper,* 
NipVpl  * 

,,  „      -LNlCKei. 

„         „    Iron.* 

„         „    Zinc.* 

„  „  Lime. 
Tartrate  of  Soda,* 
Salicine. 

lodo-sulphate  of  Quinine. 
Asparagine. 


POLARIZED    LIGHT.  Ill 

Succinic  acid. 

Stearine. 

Picrate  of  Aniline. 

Chlorate  of  Cinchoniiie. 

Borate  of  Soda. 

Margarine. 

Quinidine. 

Santonine. 

Sugar. 

Uric  acid. 

Chromate  of  Potash. 

Paraffine. 

Platino-cyanide  of  Magnesium. 

The  beginner  need  not  make  use  of  a  large 
quantity  of  the  material  he  is  about  to  experiment 
with,  and  the  only  apparatus  he  requires  is  a  small 
test-tube  about  4  inches  long  and  half  an  inch  in 
diameter.  Fill  about  1  inch  of  this  with  distilled 
water  (if  the  crystals  are  soluble  in  water),  add 
two  or  three  crystals,  and  dissolve  with  heat  if 
necessary ;  take  up  a  small  quantity  with  a  dip- 
ping tube  and  drop  it  on  a  perfectly  clean  slide  or 
cover.  It  is  as  well  to  prepare  several  slides, 
allowing  some  to  dry  slowly,  and  others  to  be 
evaporated  over  a  spirit-lamp. 

One  of  the  most  beautiful  examples  of  crystalli- 
zation is  that  of  Salicine,and  as  merely  recrystallizing 
it  from  its  solution  will  only  result  in  disappoint- 
ment, we  will  give  explicit  directions  for  the  pro- 
duction of  the  rosette  form  of  crystals  as  in  Fig.  2, 
plate  9.  A  saturated  solution  of  the  alkaloid  must 
be  prepared,  a  drop  of  the  solution  placed  on  a 
glass  cover,  and  held  over  a  spirit-lamp  until  it 
not  only  evaporates  the  water,  but  melts  the  re- 
siduum. The  cover  must  now  be  put  in  a  cool 
place,  and  protected  from  dust.  If  the  cover  is 


112  A    HALF-HOUR    WITH 

examined  after  the  lapse  of  a  short  time,  small 
circular,  semi-transparent  spots  will  be  found  scat- 
tered over  the  surface.  Further  crystallization 
may  be  prevented  by  warming  it  and  mounting  in 
Canada  balsam  or  Dammar. 

The  iodo-sulphate  of  Quinine  (Fig.  1,  plato  9), 
also  requires  special  preparation. 

These  crystals  were  first  prepared,  and  their 
optical  properties  described  by  Dr.  Herapath,  of 
Bristol.  The  following  are  his  own  directions  for 
making  them  : — 

Mix  3  drachms  of  pure  acetic  acid  with  1 
drachm  of  alcohol ;  add  to  these  6  drops  of  diluted 
sulphuric  acid  (1  to  9). 

One  drop  of  this  fluid  is  to  be  placed  on  a  glass 
slide,  and  the  merest  atom  of  quinine  added, 
time  given  for  solution  to  take  place;  then,  upon 
the  tip  of  a  very  fine  glass  rod,  a  very  minute 
drop  of  tincture  of  iodine  is  to  be  added.  The 
first  effect  is  the  production  of  the  yellow  or 
cinnamon-brown  coloured,  composed  of  iodine  and 
quinine,  which  shows  itself  as  a  small  circular 
spot ;  while  the  alcohol  separates  in  little  drops, 
which,  by  a  sort  of  repulsive  movement,  drive  the 
fluid  away.  After  a  time  the  acid  liquid  again 
ilows  over  the  spot,  and  the  polarizing  crystals  of 
iodo-sulphate  of  quinine  are  slowly  produced  with- 
out the  aid  of  heat. 

Dr.  Herapath  also  succeeded  in  producing  these 
crystals  in  large  plates,  which  could  be  used  in 
place  of  tourmalines,  and  they  are  called  artificial 
tourmalines  or  Herapathite. 

Santonine  is  an  alkaloid  prepared  from  the 
so-called  Semen  Cynce,  or  worm  seed.  It  is  soluble 
in  alcohol,  chloroform,  and  water.  Each  solvent 
alters  the  character  of  crystal.  With  chloroform 
the  crystals  assume  a  lace-like  appearance;  crystal- 


POLARIZED   LIGHT.  113 

lized  from  water,  they  arrange  themselves  in  tufts, 
composed  of  small  oblong  plates,  arranged  round 
a  nucleus.  Santonine  may  also  be  crystallized  on 
a  hot  slide,  when  crystals  radiating  from  a  centre 
will  be  formed. 

Asparagine,  an  alkaloid  obtained  from  asparagus, 
crystallizes  in  diamonds  similar  to  the  crystals  of 
Aspartic  acid,  shown  in  fig.  3,  plate  9.  This  acic- 
is  obtained  from  asparagine,  but  is  difficult  to  pro- 
cure ;  a  specimen  had  therefore  better  be  procured 
from  the  dealers  in  microscopic  objects. 

Succinic  acid  is  obtained  by  the  distillation  of 
amber. 

The  preparation  of  slides  of  paraffine,  stearine, 
margarine,  and  wax  offer  no  difficulties  to  the 
beginner ;  all  that  is  necessary  is  to  place  a  small 
piece  of  the  material  on  a  warm  slide ;  then  place 
a  thin  cover  over  it,  heat  the  slide  until  the 
substance  melts,  press  down  the  cover,  continuing 
the  pressure  until  the  slide  is  cold;  or  the  slide 
can  be  placed  at  once  on  the  stage  of  the  micro- 
scope, and  the  gradual  crystallization  observed  as 
the  slide  becomes  cold. 

The  medium  in  which  a  salt  is  dissolved  affects 
the  form  and  arrangement  of  the  crystals  when 
it  is  recrystallized.  The  media  affording  the  best 
results  are  gelatine,  gum,  and  albumen. 

The  following  method  will  enable  the  young 
student  to  add  many  beautiful  slides  to  his  collec- 
tion of  polariscope  objects.  Dissolve,  with  heat,  a 
small  piece  of  gelatine  in  the  test-tube  before  de- 
scribed, using  a  similar  quantity  of  distilled  water. 
In  another  test-tube  make  a  saturated  solution 
of  the  salt  (sulphate  of  copper,  for  example),  add  a 
few  drops  to  the  gelatine  (mix  thoroughly,  but 
avoid  forming  bubbles,  stirring  it  with  a  glass  rod 
or  piece  of  platinum  wire) ;  spread  a  drop  on  a 
I 


114  A    HALF-HOUR    WITH 

glass  cover,  set  aside  in  a  cool  place  to  dry  ;  this 
will  usually  take  about  half  an  hour.  If  the 
experiment  has  been  successful,  the  crystals  will 
appear  like  fern  fronds.  (See  fig.  4,  plate  9.) 

This  figure  will  give  some  idea  of  the  elegance  of 
form  and  beauty  of  colour ;  but  it  is  beyond  the 
skill  of  any  artist  to  do  justice  to  the  beauty  of 
a  good  slide.  The  sulphates  of  nickel  and  iron  are 
also  very  good  when  crystallized  out  of  gelatine. 

"With  chlorate  of  potash,  a  totally  different  form 
of  crystallization  is  produced,  the  crystals  being 
tabular  and  large.  A  very  remarkable  effect  is 
produced  when  a  small  quantity  of  a  solution 
of  barium  is  added  ;  the  barium  will  be  found 
to  have  crystallized  in  small  moss-like  tufts  at 
the  angles.  Chloride  of  barium  mixed  with 
the  gelatine  solution  assumes  a  dendritic  form, 
somewhat  resembling  sulphate  of  copper,  but 
polarizes  differently.  Gum  arabic  may  be  substi- 
tuted for  gelatine ;  the  modus  operand*  is,  how- 
ever, similar  ;  albumen  (white  of  egg)  requires  to 
be  dried  before  it  is  added  to  the  distilled  water, 
which  must  be  only  slightly  warmed.  The  stu- 
dent cannot  do  better  than  try  the  effect  of  the 
different  media  ;  some  salts  do  better  with  gela- 
tine, others  with  gum  ;  for  example,  he  will  be 
able  to  produce  more  effective  slides  of  tartrate  of 
soda  with  gum  than  gelatine. 

Platino-cyanide  of  Magnesium  must  be  prepared 
without  heat,  as  warmth  alters  the  colour  of  the 
crystals.  "We  have  obtained  the  best  results  by 
adding  a  few  crystals  to  a  drop  of  the  gelatine  solu- 
tion previously  placed  on  the  slide,  stirring  them 
with  a  stout  bristle  until  dissolved,  and  then  allow- 
ing them  to  slowly  recrystallize.  These  crystals, 
like  the  iodo-sulphate  of  Quinine,  will  analyze  a 
polarized  ray.  They  are  best  mounted  in  dammar. 


POLARIZED    LIGHT.  115 

Very  beautiful  results  may  be  obtained  "by  a 
mixture  of  two  or  more  salts.  Mr.  Davies,  in  the 
Quarterly  Microscopical  Journal,  Vol.  II.,  N.S., 
gives  the  following  directions  for  crystallizing  the 
double  sulphate  of  copper  and  magnesia.  Make 
nearly  a  saturated  solution  of  the  two  salts,  place 
a  drop  on  a  slide  and  dry  rapidly,  allowing  the 
slide  to  become  hot  enough  to  fuse  the  salt, 
which  will  now  appear  as  an  amorphous  film  on 
the  slide.  On  slowly  cooling,  the  salt  will  absorb 
moisture  from  the  surrounding  air,  and  crystalli- 
zation will  commence  from  various  points,  assum- 
ing the  appearance  of  flowers.  As  soon  as  these 
"  flowers "  are  perfected  the  slide  should  be 
slightly  warmed  and  a  little  of  pure  Canada  balsam 
dropped  upon  it,  and  covered  with  the  usual  thin 
glass  cover. 

Sugar  requires  a  somewhat  different  treatment 
to  any  of  the  crystals  previously  described,  and 
the  tyro's  first  attempts  will  probably  result  in 
disappointment.  The  best  for  the  purpose  is  the 
white  "  stone  sugar."  Dissolve  this  in  water, 
using  enough  to  form  a  thick  syrup ;  spread  a 
drop  on  a  cover,  drying  it  quietly  over  a  spirit- 
lamp  ;  when  dry  place  it  in  a  damp  cellar  cr 
cupboard.  In  the  course  of  twenty-four  hours 
crystallization  will  have  taken  place.  The  cover 
should  now  be  mounted  in  balsam. 

Passing  from  the  inorganic  to  organic  we  pro- 
ceed to  give  a  few  hints  on  the  preparation  of 
specimens  from  vegetable  and  animal  kingdoms. 

The  following  are  a  few  of  the  objects  from  the 
former  which  the  student  will  have  little  difficulty 
in  obtaining  : — 

Potato  starch. 
Tous  les  mois  ditto. 
i2 


116  A   HALF-HOUR   WITH 

Cotton  fibre. 

Hairs  and  scales  from  leaves. 

Longitudinal  sections  of  wood. 

The  first-named  on  our  list  can  be  very  easily 
procured  by  scraping  a  potato,  and  then  shaking 
the  pulp  in  a  test-tube  with  water,  to  which  ;i 
small  quantity  of  soda  has  been  added.  The 
starch  will  rapidly  subside,  and  the  fibrous  matter, 
&c.,  can  be  poured  off.  The  washing  should  be 
repeated  until  the  starch  is  left  perfectly  pure. 
Starch  for  polarizing  purposes  requires  to  be 
mounted  in  Canada  balsam.  The  hairs  and  scales 
of  plants  require  no  preparation  for  mounting. 
The  scales  of  Eleagnus  or  ffippophce  rhamnoides 
(sea  buckthorn)  (Fig.  6,  pi.  9),  are  easily  procured, 
and  offer  no  difficulty  to  the  young  manipulator, 
merely  requiring  to  be  detached  from  the  cuticle 
of  the  leaf  with  the  point  of  a  knife  or  lancet,  and 
afterwards  transferred  to  a  drop  of  water,  to 
which  a  minute  quantity  of  gum  has  been  pre- 
viously added,  when  dry,  mount  in  balsam. 

The  following  list  contains  a  few  of  the  objects 
from  the  animal  kingdom  : — 

Fish  scales. 

Palates  of  Mollusca. 

Hairs. 

Quill. 

Horn. 

Whalebone. 

Fish  scales  are  so  well  known  that  no  difficulty 
can  arise  in  obtaining  specimens,  with  the  excep- 
tion of  those  from  the  eel,  which  do  not  occur  on 
the  surface,  but  will  be  found  imbedded  in  the 
skin ;  they  may  be  obtained  by  picking  the  skit 
with  the  point  of  a  needle,  previously  scraping  off 
the  mucus. 


POLARIZED    LIGHT.  117 

The  palates  of  mollusca,  as  polariscope  objects, 
are  not  as  a  rule  very  effective,  that  of  the  common 
Whelk  excepted. 

Hairs  are  worthy  of  notice  for  polarizing  pur- 
poses, as  they  usually  display  a  considerable  amount 
of  colour.  While  horsehair  and  grey  human  hair 
(Fig.  5,  pi.  9)  are  perhaps  the  best  for  the  student's 
purpose. 

The  structure  of  Rhinoceros  horn  and  whale- 
bone is  well  displayed  when  polarized,  but  they 
are  difficult  to  prepare,  and  it  would  be  better  to 
purchase  them  of  the  dealers  in  microscopic  pre- 
parations. 

The  mineral  kingdom  affords  but  few  objects 
that  can  be  prepared  by  the  amateur,  although  no 
collection  of  polariscope  objects  would  be  com- 
plete without  one  or  more  sections  of  agate  and 
chalcedony;  and,  like  the  objects  previously 
named,  must  be  obtained  from  the  dealer.  The 
young  microscopist  should,  however,  obtain  from 
some  optician  a  piece  of  the  so-called  Brazilian 
pebble  (really  transparent  quartz),  and  break  it 
up  into  small  fragments  :  many  of  these,  when 
mounted,  display  very  beautiful  coloured  rings. 

A  few  words  may  perhaps  be  necessary  as  to  the 
mode  of  procedure  in  mounting  specimens  of 
crystal.  We  have  in  several  instances  directed 
the  solution  to  be  placed  on  the  cover  ;  our  reason 
for  doing  so  is,  in  order  to  avoid  the  application 
of  any  great  degree  of  heat,  and  at  the  same  time 
using  tolerably  hard  balsam. 

The  plan  we  adopt  is  as  follows.  Place  a  drop 
of  pure  balsam  on  the  centre  of  a  slide,  harden 
over  the  lamp  (it  will  be  sufficiently  so  if  the 
nail  slightly  indents  it  when  cold) ;  now  drop  a 
little  turpentine  on  the  prepared  cover,  holding  it 
as  close  as  possible  to  the  edge  with  the  forceps, 


118      A    HALF-HOUK   WITH    POLARIZED    LIGHT. 

rewarm  the  slide,  and  apply  the  opposite  edge  of 
the  cover  to  the  edge  of  the  balsam,  and  allow 
the  cover  to  fall  gradually  down ;  when  the 
glass  disc  is  covered  by  the  balsam,  press  care- 
fully until  all  the  superfluous  balsam  is  squeezed 
out. 

We  must  now,  however,  draw  our  last  half-hour 
to  a  close.  All  we  have  attempted  has  been  in  the 
"way  of  introduction.  We  have  only  described  those 
things  which  are  most  easily  obtained,- and  we  have 
sought  rather  to  create  a  desire  for  further  know- 
ledge, than  to  impart  an  exhaustive  amount  of 
information  on  any  one  subject. 

Those  who  have  properly  apprehended  our  re- 
marks will  see  that  there  is  not  a  distinct  science 
of  microscopic  objects,  but  that  these  objects  belong 
to  various  departments  of  science,  whose  great  facts 
and  principles  must  be  studied  from  works  devoted 
to  them.  The  Microscope  is  in  fact  an  instrument 
to  assist  the  eyes  in  the  investigation  of  the  facts 
of  structure  and  function,  wherever  they  may  occur 
in  the  great  field  of  nature;  and  that  inquirer 
must  have  a  very  limited  view  of  the  nature  of 
science,  who  supposes  either  that  the  Microscope  is 
the  only  instrument  of  research,  or  that  any  in- 
vestigation, where  its  aid  reveals  new  facts,  can  be 
successfully  carried  on  without  it. 


APPENDIX. 

BY   THOMAS   KETTERINGHAM. 


THE  PREPARATION  AND  MOUNTING  OP 
OBJECTS. 

THE  majority  of  objects  exhibited  by  the  Microscope  require 
some  kind  of  preparation  before  they  can  be  satisfactorily 
shown,  or  their  form  and  structure  properly  made  out.  To 
convince  the  beginner  of  this,  let  him  take  the  leg  of  any 
insect,  and,  without  previous  preparation,  place  it  under  his 
Microscope,  and  what  does  he  see  ?  A  dark  opaque  body, 
fringed  with  hair,  and  exceedingly  indistinct.  But  let  him 
view  the  same  object  prepared  and  permanently  mounted, 
and  he  will  then  regard  it  with  delight.  That  beautiful  limb, 
rendered  transparent  by  the  process  it  has  undergone,  now 
lies  before  him,  rich  in  colour,  wonderful  in  the  delicate 
articulation  of  its  joints,  exquisite  in  its  finish,  armed  at 
its  extremities  with  two  sharp  claws  equally  serviceable  for 
progression  or  aggression,  and  furnished,  in  many  instances, 
with  pads  (pulvilli)  (see  plate  7,  figures  205,  206),  which 
enable  the  insect  to  walk  with  ease  and  safety  on  the 
smoothest  surface.  If  the  beginner  has  a  true  love  for  the 
study  of  the  Microscope,  he  will  be  glad  of  information 
respecting  the  method  pursued  in  dissecting  and  preserving 
microscopic  objects,  nor  will  he  rest  satisfied  until  he  has 
acquired  some  knowledge  of  the  art.  We  will  briefly  point 
out  a  few  of  the  advantages  possessed  by  those  who  are  able 
to  prepare  specimens  for  themselves. 

Objects  well  mounted  will  remain  uninjured  for  years,  and 
will  continue  to  retain  their  colour  and  structure  in  all  their 
original  freshness. 

They  can  be  exhibited  at  all  times  to  one's  friends,  and 
may  be  studied  with  advantage  whenever  an  opportunity 


120  APPENDIX. 

By  the  practice  of  dissection  such  a  knowledge  is  gained 
of  the  varied  forms  and  internal  organization  of  minute 
creatures  as  can  be  obtained  in  no  other  way. 

There  are  doubtless  many  who,  possessing  a  small  Micro- 
scope, are  unable  by  reason  of  their  limited  means  to  expend 
money  in  the  purchase  of  ready-prepared  specimens.  To 
such,  a  few  plain  directions,  if  followed,  will  be  of  service, 
and  will  enable  them  to  prepare  their  own. 

The  materials  necessary  for  the  beginner  are  few,  and  not 
expensive.  In  fact,  the  fewer  the  better  ;  for  a  multiplicity 
is  apt  only  to  cause  confusion.  The  following  will  be  found 
sufficient  for  all  ordinary  purposes,  and  may  be  obtained  at 
any  optician's. 

Bottle  of  new  Canada  balsam. 

Bottle  of  gold-size. 

Bottle  of  Brunswick  black. 

Spirits  of  turpentine — small  quantity. 

Spirits  of  wine — small  quantity. 

Solution  of  caustic  potash  (liquor  potas$afy. 

Ether— a  small  bottle. 

Empty  pomatum-pots,  with  covers,  for  holding  objects 
•while  in  pickle. 

Half  a  dozen  needles  mounted  in  handles  of  camel-hair 
brushes. 

Pair  of  brass  forceps. 

Two  small  scalpels. 

Pair  of  fine-pointed  scissors. 

Camel-hair  pencils — half  a  dozen. 

Slips  of  plate-glass,  one  inch  by  three  inches — two  dozen. 

Thin  glass  covers,  cut  into  squares  and  circles — half  au 
ounce. 

We  will  suppose  that  the  beginner,  having  purchased  the 
necessary  materials,  is  about  to  make  his  first  attempt.  Let 
him  attend  to  the  following  advice,  and  he  will  escape  many 
failures. 

He  must  bring  to  his  work  a  mind  cool  and  collected  ; 
hands  clean  and  free  from  grease.  Let  him  place  everything 
he  may  require  close  at  hand,  or  within  his  reach.  A  stock 
of  clean  slides  and  covers  must  always  be  ready  for  use.  He 
must  keep  his  needles,  scissors,  and  scalpels  scrupulously 
clean.  An  ingenious  youth  will  readily  construct  for  himself 
a  box  to  contain  all  his  tools.  Cleanliness  is  so  essential  to 
success,  that  too  much  stress  cannot  be  laid  upon  it.  All 
fluids  should  be  filtered  and  kept  in  well-corked  phials.  A 
bell-glass,  which  may  be  purchased  for  a  few  pence,  will  be 
found  exceedingly  useful  in  covering  an  object  when  any  delay 


APPENDIX.  121 

takes  place  in  the  mounting.  For  want  of  it,  many  specimens- 
have  been  spoilt  by  the  intrusion  of  particles  of  dust,  soot, 
and  other  foreign  substances.  Let  the  table  on  which  the 
operator  is  at  work  be  steady,  and  placed  in  a  good  light, 
and,  if  possible,  in  a  room  free  from  intrusion. 

WINGS  OF  INSECTS. — Perhaps  these  are  the  easiest  objects 
upon. which  the  beginner  can  try  his  "'prentice  hand."  Here 
little  skill  is  required.  Select  a  bee,  or  wasp,  and  with  your 
fine  scissors  sever  the  wing  from  its  body  ;  wash  it  with  a 
camel-hair  brush  in  some  warm  water,  and  place  it  between 
two  slips  of  glass,  previously  cleaned,  which  may  be  pressed 
together  by  a  letter-clip,  or  an  American  clothes- peg  ;  place 
it  in  a  warm  corner  for  a  few  days  ;  when  quite  dry,  remove 
it  from  between  the  slides,  and  soak  it  for  a  short  time  in 
spirits  of  turpentine.  This  fluid  renders  the  object  more 
transparent,  frees  it  from  air-bubbles,  and  prepares  the  way 
for  a  readier  access  of  the  balsam  to  the  various  portions  of 
its  structure. 

Having  selected  from  your  stock  a  clean  slide  of  the  re- 
quisite size,  and  a  thin  glass  cover  somewhat  larger  than  the- 
object  about  to  be  mounted,  hold  them  both  up  to  the  light, 
when  any  slight  impurities  will  appear,  and  may  be  speedily 
removed  by  rubbing  the  surfaces  of  the  glass  with  a  fine 
cambric  handkerchief,  or  a  piece  of  soft  wash-leather. 
Should,  however,  a  speck  or  flaw  in  the  glass  itself  be 
found  in  the  centre  of  the  slide,  at  once  reject  it  and  choose 
another.  Remove  the  wing  with  a  pair  of  forceps  from  the 
turpentine,  and  place  it  in  the  exact  centre  of  the  slide : 
this  may  be  accomplished  by  cutting  a  stiff  piece  of  card- 
board, tin,  or  zinc,  the  size  of  the  slide,  and  punching  a 
hole,  the  edge  of  which  should  be  equally  distant  from  each 
end  and  each  side  ;  lay  the  slide  upon  it,  and  place  the 
object  in  the  circular  space  ;  you  will  thus  get  it  properly 
centred. 

Before  dropping  the  balsam  (which  should  have  been 
previously  warmed)  upon  the  specimen,  place  it  under  the 
Microscope  :  you  may  possibly  detect  some  foreign  substance, 
in  the  shape  of  a  particle  of  soot  or  a  fibre  from  your  hand- 
kerchief, in  contact  with  it  ;  remove  it  with  the  point  of  a 
needle.  Take  up  a  small  quantity  of  the  balsam  on  the  end 
of  a  small  glass  rod,  and  let  it  fall  upon  the  object ;  hold  the 
slide  for  a  few  minutes  over  the  flame  of  a  candle  or  spirit- 
lamp  at  a  distance  sufficient  to  make  it  warm,  but  not  hot ; 
the  balsam  will  gradually  spread  itself  over  and  around  the 
object:  should  air-bubbles  arise,  they  may  be  broken  by 
touching  them  with  the  point  of  a  needle  ;  they  will,  how- 


122  APPENDIX. 

<ver,  frequently  dlspeise  of  themselves  as  the  balsam  dries. 
The  thin  glass  cover,  being  warmed,  should  DOW  be  placed 
upon  the  object,  and  a  slight  pressure  applied  to  get  rid  of 
the  superfluous  balsam.  Place  the  slide  in  some  warm  spot 
to  dry  ;  an  oven  will  do  very  well,  if  the  fire  has  been  some 
time  removed  and  there  is  not  sufficient  heat  to  make  the 
balsam  boil. 

In  a  short  time  the  balsam  round  the  edges  of  the  cover 
will  be  hard  enough  to  admit  of  the  greater  part  being 
scraped  olF  with  a  knife  ;  the  remainder  may  be  got  rid  of 
by  wiping  the  slide  with  a  rag  dipped  in  turpentine  or  ether. 
The  finishing  touch  consists  in  labelling  the  object  with  its 
proper  name.  It  will  be  found  advantageous  to  place  the 
common  name  of  the  specimen  at  one  end  of  the  slide,  and 
its  scientific  name  at  the  other. 

Some  persons  prefer  covering  their  slides  with  ornamental 
paper,  which  may  be  obtained  of  almost  any  optician. 
Others  prefer  the  glass  without  any  covering  at  all.  In  the 
latter  case  the  edges  of  the  slide  should  be  ground,  the 
round  thin  glass  covers  used,  and  the  name  scratched  upon 
the  slide  with  a  writing  diamond.  In  the  former,  the  edges  . 
of  the  slide,  being  covered  with  paper,  need  not  be  ground, 
but  square  thin  covers  should  be  used  instead  of  round  ones, 
and  the  name  written  with  pen  and  ink  in  the  square  places 
allotted  at  each  end  of  the  slide. 

LEGS  OP  INSECTS  (plate  7,  figures  205,  206,  207  ;  plate  8, 
figures  215  to  219,  223,  224.— These  require  a  little  more 
preparation  than  wings  ;  and  as  they  possess  some  thick- 
ness, and  are  mostly  opaque,  besides  being  of  a  hard,  horny 
character,  they  should  be  placed  for  a  fortnight,  or  even 
longer,  in  liquor  potasses;  this  will  soften  the  tissue  and 
dissolve  the  muscles  and  other  matter  contained  within 
them,  so  that  by  gently  pressing  the  limb  between  two 
slips  of  glass,  the  interior  substance  will  gradually  escape, 
and  may  be  removed  by  repeated  washings.  The  squeezing 
process,  however,  must  be  conducted  gently,  to  prevent 
any  rupture  :  perhaps  the  best  plan  is  to  plunge  the  slips 
of  glass  into  a  basin  of  clean  water,  when  all  impurities 
oozing  out  from  the  pressure  will  sink  to  the  bottom. 
Should  the  leg  not  be  sufficiently  softened  to  be  squeezed 
quite  flat,  it  must  be  again  placed  in  the  solution  for 
a  longer  period,  until  this  result  be  obtained.  On  re- 
moving it  from  the  potash,  it  should  be  well  washed  with 
a  camel-hair  pencil  in  clean  \\ater,  placed  between  two  slips, 
held  together  by  an  American  clothes-peg  \\  ith  a  good  stiff 


Al'l'ENDIX.  123 

spriug.  If  placed  in  a  warm  corner,  a  few  days  will  le 
sufficient  to  dry  it  thoroughly  :  afterwards  soak  it  in  spirits 
of  turpentine  ;  the  time  of  immersion  to  be  regulated  by  the 
opacity  of  the  object. 

The  directions  for  mounting  in  balsam  are  precisely 
the  same  as  those  given  for  the  wings  of  insects.  Care 
should  be  taken  not  to  heat  the  balsam  too  hot,  as  it  will 
invariably  destroy  delicate  specimens  by  curling  them  up. 
I  n  tough  horny  structures,  such  as  the  wing-cases  of  beetles, 
&c.,  heat  is  sometimes  an  advantage,  and  there  are  a  few 
structures  that  show  to  advantage  when  the  balsam  has  been 
heated  to  a  boiling  pitch  ;  but  for  the  majority  of  objects,  a 
gentle  warmth  is  all  that  is  required. 

OVIPOSITORS  AND  STINGS  (plate  7,  figure  200)  are  more 
difficult  to  prepare,  and  require  some  amount  of  dissection 
before  they  can  be  properly  displayed.  To  do  this,  some 
degree  of  skill  is  necessary,  and  a  knowledge  of  insect 
anatomy,  which  can  be  acquired  only  by  study  and  practice. 
As  a  rule,  all  dissections  should  be  carried  on  as  far  as 
possible  with  the  naked  eye ;  when  this  has  been  accom- 
plished, we  must  then  seek  the  aid  of  lenses. 

The  object-glasses  of  one's  Microscope  are  the  best  that 
can  be  used  for  the  purpose.  An  inch  lens  will  be  found 
especially  fitted  for  the  work.  A  simple  Microscope,  pro- 
vided with  a  broad  stage,  and  an  arm  movable  by  rack  and 
pinion,  for  carrying  the  lenses,  is  the  kind  of  instrument 
usually  employed.  It  should  be  strongly  made,  and  capable 
of  bearing  a  good  deal  of  rough  usage. 

Dissections  may  be  carried  on  under  the  compound  Micro- 
scope ;  but  we  do  not  think  the  beginner  would  succeed,  aa 
objects  become  inverted  and  motion  reversed  when  seen 
through  this  instrument.  If,  however,  it  be  provided  with 
an  erector,  this  difficulty  is  overcome  by  the  object  being 
brought  into  the  same  position  that  it  occupies  when  seen  by 
the  n;xked  eye. 

As  most  dissections  are  carried  on  under  water,  some  kind 
of  shallow  trough  is  necessary  to  contain  it :  watch-glasses 
answer  the  purpose  remarkably  well.  The  small  white 
dishes  and  covers  used  for  rubbing  up  colours  will  be  found 
very  useful  ;  also  some  cork  bungs  on  which  to  pin  the 
object ;  and  these  last  should  have  their  under  sides  loaded 
with  lead  to  sink  them  in  fluid.  A  great  many  delicate 
dissections  may,  however,  be  made  in  a  drop  of  water  placed, 
on  a  slip  of  glass  ;  but  for  all  objects  of  large  size,  the  trcugh, 
or  some  similar  contrivance,  will  be  necessary. 


121 


APPENDIX. 


All  insects  that  have  been  killed  a  long  iime,  nnd  whose 
bodies  are  hard  and  brittle,  may  be  softened  by  immersing 
them  in  the  solution  already  mentioned. 

The  sting  of  the  bee,  wasp,  hornet,  and  the  ovipositors  of 
many  flie.s,  especially  the  ichneumons,  are  very  similar  in 
their  structure,  and  are  generally  found  at  the  termination 
of  the  abdomen,  from  which  they  may  be  obtained  by  first 
slitting  open  the  body  of  the  insect  with  the  fine  scissors, 
and  afterwards  removing  the  sting  by  using  the  scalpel  and 
needles.  One  or  two  of  the  latter  should  have  their  points 
curved,  which  may  easily  be  accomplished  by  heating  the 
ends  red-hot  in  the  flame  of  a  candle,  and  bending  them 
with  a  pair  of  small  pincers.  At  first  sight  the  sting  pre- 
sents nothing  to  the  eye  but  a  horny  sheath,  tapering  to  a 
point,  with  a  slit  broadest  at  its  base  and  running  down  the 
entire  length  ;  within  this  sheath,  on  each  side,  lies  a  barbed, 
sharp-pointed  spear,  in  large  insects  capable  of  inflicting  a 
severe  wound,  while  the  tube  in  which  they  are  lodged 
acts  as  a  steadying  rod,  and  as  a  channel  to  conduct  a 
virulent  poison  to  the  wound.  The  bag  containing  the 
poison  is  placed  at  the  root  of  the  sting,  and  is  connected 
by  a  narrow  neck  with  the  sheath.  The  difficulty  in  the 
dissection  of  the  sting  lies  in  getting  the  barbed  points  out 
of  the  sheath  and  placing  them  on  each  side  of  it.  The 
following  is  the  method  employed  by  the  writer.  The  sting 
is  placed  in  potash  until  it  loses  some  of  its  rigidity  ;  it  is 
then  transferred  to  a  slip  of  glass  or  earthenware  trough. 
The  curved  needle-points  are  essential  here.  With  one,  hold 
the  object  firmly  on  the  stage  of  the  Microscope,  insert  the 
point  of  the  other  into  the  opening  at  the  base  of  the  sheath 
where  it  is  largest,  and  gradually  draw  the  point  down  the 
tube  ;  this  will  make  the  opening  wider,  and  dislodge  the 
barbs  ;  arrange  them  on  each  side  of  the  sheath,  place  the 
sting  between  two  glass  slips  subject  to  pressure.  When 
dry,  soak  it  for  a  few  days  in  turpentine,  and  mount  in 
balsam  in  the  usual  manner.  A  good  specimen  ought 
to  show  the  barbs  very  distinctly  on  each  side  of  the 
sheath. 

It  will  be  found  useful  to  the  student  to  prepare  three 
specimens  of  this  organ  : — 

1st.  The  whole  abdomen,  showing  the  position  the  sting 
occupies  within  it. 

2nd.  The  sting  with  the  barbs  lying  within  the  sheath. 

3rd.  The  barbs  pulled  out  of  the  sheath  and  placed  on 
each  side  of  it. 

Three  such  specimens  well  mounted  will  enable  the  student 


APPENDIX.  125 

to  study  the  structure  of  this  curious  organ  with  advan- 
tage. 

SPIRACLES  (plate  7,  figures  212,  213). — These  do  not  re- 
quire much  dissection.  They  are  generally  found  on  each 
side  of  the  abdomen,  almost  every  segment  of  which  possesses 
a  pair.  Excellent  specimens  are  furnished  by  the  dytiscus, 
bee,  blowfly,  cockchafer,  and  silkworm.  To  prepare  them, 
separate  from  the  thorax  the  abdominal  portion  of  the 
insect,  and  slit  it  down  the  centre  with  the  fine-pointed 
scissors,  draw  out  the  viscera,  &c.,  with  the  curved  needles. 
The  air-tubes  adhering  to  the  spiracles  may  be  detached  by 
cutting  them  away  with  the  scissors.  Thoroughly  cleanse 
the  horny  cuticle  by  repeated  washings,  spread  it  out  flat 
between  two  slips  of  glass  ;  when  dry,  immerse  it  in  spirits 
of  wine  or  turpentine  for  a  few  days,  and  mount  it  in  balsam. 
In  this  manner  the  whole  of  the  spiracles  of  an  insect,  run- 
ning down  each  side  of  the  abdomen,  will  be  displayed. 

TRACHEAE  (plate  8,  figure  222). — The  best  method  we  are 
a-cquainted  with  for  obtaining  the  air-tubes  of  insects  is  that 
recommended  by  Professor  Quekett : — 

"By  far  the  most  simple  method  of  procuring  a  perfect 
system  of  tracheal  tubes  from  the  larva  of  an  insect,  is  to 
make  a  small  opening  in  its  body,  and  then  to  place  it  in 
strong  acetic  acid  :  this  will  soften  or  decompose  all  the 
viscera,  and  the  trachea?  may  then  be  well  washed  with  the 
syringe,  and  removed  from  the  body  with  the  greatest  facility, 
by  cutting  away  the  connections  of  the  main  tubes  with  the 
spiracles  by  means  of  the  fine-pointed  scissors.  In  order  to 
get  them  upon  the  slide,  this  must  be  put  into  the  fluid  and 
the  trachea?  floated  upon  it,  after  which  they  may  be  laid 
•out  in  their  proper  position,  then  dried,  and  mounted  in 
balsam." 

The  best  specimens  are  found  in  the  larva  of  the  dytiscua 
And  cockchafer,  and  in  the  blowfly,  goat-moth,  silkworm,  and 
house-cricket. 

GIZZARDS  (plate  8,  figures  220,  a,  b  ;  221,  a,  6). — Most  of 
^the  insects  from  which  these  organs  are  procured  being  of 
large  size,  it  will  be  necessary  to  secure  them  to  one  of  the 
loaded  corks  by  small  pins.  The  dissection  should  be  made 
in  one  of  the  shallow  troughs,  filled  with  weak  spirits  and 
water.  Cut  the  insect  open  ;  the  stomach  will  float  out 
with  the  gizzard  attached  to  it,  in  the  shape  of  a  small 
bulbous  expansion  of  the  size  of  a  pea.  Insert  the  fine 
point  of  the  scissors,  and  cut  it  open  ;  the  interior  will  be 
found  full  of  food  in  process  of  trituration.  Empty  the 
contents  of  the  gizzard,  and  wash  it  out  well;  place  it  for 


12  3  APPENDIX. 

a  few  days  in  the  solution  of  potash  :  and,  finally,  cleanse 
it  with  some  warm  \\ater  and  a  camel-hair  brush.  Spread 
it  out  flat  between  slips  of  glass  ;  when  dry,  place  it  in 
turpentine  for  a  week,  and  afterwards  mount  it  in 
balsam. 

The  best  specimens  for  displaying  the  horny  teetli  with 
which  the  gizzard  is  furnished  are  obtained  from  crickets, 
grasshoppers,  and  cockroaches. 

PALATES  (plate  6,  figures  171,  172,  173,  174). —These, 
consist  of  a  narrow  kind  of  tongue,  armed  with  a  series  of 
horny  teeth,  placed  in  regular  rows.  The  whelk,  limpet^ 
periwinkle,  garden-snail,  and  the  snails  found  in  our  cellais 
and  aquariums,  are  all  furnished  with  this  peculiar  appara- 
tus, which  may  be  obtained  by  laying  open  the  body  with 
the  scalpel  or  scissors.  It  will  generally  be  found  curled  up- 
near  the  head,  and  may  be  distinguished  by  its  ribbon-like 
appearance :  patience  and  skill  are  necessary  to  extract  it 
from  the  surrounding  mass.  When  properly  cleaned,  it  may 
be  at  once  pressed  flat  and  dried  between  slips  of  glass. 
Many  palates  polarize  well  when  mounted  in  balsam  ;  but 
if  not  intended  for  polarization,  they  shculd  be  mounted  in 
a  preservative  fluid,  composed  of  five  grains  of  salt  to  one 
ounce  of  water. 

TONGUES,  PROBOSCES,  MANDIBLES,  AND  ANTENNAE 
(plate  7,  figures  197, 199,  202  to  204)  are  amongst  the  most 
beautiful  objects  exhibited  by  the  Microscope.  Many  of 
these,  besides  the  ligula,  possess  several  sharp  lancets  for 
puncturing  the  skin  of  animals  from  whom  they  derive  their 
sustenance.  To  arrange  these  organs  so  that  each  part 
may  be  clearly  seen,  requires  a  good  deal  of  delicate  mani- 
pulation. It  is  generally  more  satisfactory  to  mount  the 
whole  head  of  the  insect.  To  accomplish  this,  it  must  be 
softened  by  immersion  in  liquor  potassce  for  some  time,  and 
the  interior  substance  got  rid  of  by  pressure.  To  dry  it 
flat,  place  it  between  two  slips  of  glass,  which  should  be  held 
together  by  a  spring-clip  ;  soak  it  for  a  fortnight  or  longer 
in  turpentine,  until  it  becomes  transparent,  and  then  mount 
it  in  balsam. 

The  head  of  the  bee,  wasp,  dronefly,  blowfly,  and  gadfly, 
are  all  excellent  examples  of  the  varied  structures  of  these 
suctorial  organs. 

EYES  (plate  7,  figures  208,  208«,  210). — The  compound 
eyes  of  insects,  for  the  display  of  their  numerous  facets, 
should  be  dissected  from  the  head,  and  macerated  in  fluid. 
The  black  pigment  lining  the  interior  may  be  got  rid  of  by 
washing  it  away  with  a  camel-hair  brush.  When  quite 


APPENDIX.  1 

clean,  the  cornea  may  be  dried  and  flattened  between  two 
slips  of  glass.  In  practice,  however,  the  cornea,  from  its 
sphericity,  will  be  found  to  have  a  tendency  to  fold  in  plaits, 
or  to  split  in  halves.  To  remedy  this,  cut  with  the  fine 
scissors  a  few  notches  round  its  edges  ;  it  may  then  be 
flattened  without  danger  of  its  either  wrinkling  or  splitting. 
When  the  cornea  is  very  transparent  it  should  be  mounted 
in  a  cell  with  some  kind  of  preservative  fluid  (spirit  and 
water  will  do  very  well),  otherwise  the  structure  will  be  lost 
if  mounted  in  balsam,  the  tendency  of  that  substance  being 
to  add  transparency  to  every  object  with  which  it  comes  in 
contact.  But  there  are  many  insects  in  whose  eyes  the 
hexagonal  facets  are  strongly  marked  :  all  such  will  show- 
best  when  mounted  in  balsam. 

HAIKS  (plate  7,  figures  184  to  191).— These  may  be 
mounted  either  in  fluid  or  balsam,  first  taking  the  precaution 
to  cleanse  them  from  fatty  matter  by  placing  them  in  ether. 
If  the  hair  be  coarse  and  opaque,  mount  it  in  balsam ;  if 
fine  and  transparent,  it  should  be  mounted  in  a  cell,  with 
some  weak  spirit. 

Sections  of  hair  are  made  by  gluing  hairs  into  a  bundle, 
and  placing  it  in  a  machine  for  making  sections.  By  means 
of  a  sharp  knife  which  traverses  the  surface,  the  thinnest 
slices  may  be  cut,  and  each  individual  section  afterwards  ean 
be  separated  in  fluid.  To  select  the  thinnest  and  best,  place 
them  under  the  Microscope.  The  point  of  a  camel-hair 
pencil  will  be  found  the  best  instrument  for  transferring 
them  to  a  clean  slide.  When  dry,  mount  them  in  balsam,  as 
usual.  Some  very  good  sections  of  the  hairs  of  the  beard 
may  be  obtained  by  passing  the  razor  over  the  face  a  few- 
minutes  after  having  shaved. 

SCALES  OP  FISH  (plate  6,  figures  178  to  180). — These 
dermal  appendages  may  be  detached'  from  the  skin  by  a 
knife  ;  and  if  to  be  viewed  as  opaque  objects,  may  be  dried 
and  mounted  with  no  other  preparation  than  cementing  over 
them  a  thin  glass  cover.  If  intended  to  be  viewed  as  trans- 
parent objects,  the  scales  should  be  properly  cleaned,  dried, 
and  mounted  in  balsam  ;  but  the  most  satisfactory  way  of 
exhibiting  their  structure  is  to  mount  them  in  a  cell  with 
some  preservative  fluid. 

SCALES  OF  BUTTERFLIES,  MOTHS,  &c.  (plate  8,  figures  225 
to  229). — Select  the  wing  of  a  living  or  recently-killed  insect, 
gently  press  it  on  the  centre  of  a  clean  glass  slide.  On  re- 
moving the  wing,  numerous  scales  will  be  seen  adhering  to 
the  slide  ;  place  over  them  one  of  the  thin  glass  covers,  and 
cement  it  down  by  tipping  lightly  the  edges  with  gold  size. 


128  APPENDIX. 

Specimens  should  be  taken  from  various  parts  of  the  wings 
-of  the  same  insect,  as  the  form  of  the  scales  vary  according 
to  the  position  they  occupy  in  the  wing. 

SECTIONS  or  BONE  (plate  8,  figure  232). — All  hard  and 
brittle  substances  from  which  thin  slices  cannot  be  made  by 
a  sharp  knife,  must  be  reduced  to  a  transparent  thinness 
by  the  process  of  grinding  down.  Having  selected  the  bone 
from  which  the  section  is  about  to  be  made,  a  thin  slice 
should  be  cut  from  it  with  a  fine  saw.  At  first  the  section, 
may  be  held  by  the  fingers  while  grinding  down  one  of  its 
surfaces  on  a  coarse  stone  ;  but  when  it  approaches  the  thin- 
ness of  a  shilling,  it  must  be  cemented  by  some  old  and  tough 
Canada  balsam  to  a  slip  of  glass.  Upon  the  perfect  adhesion 
of  the  section  to  the  slide  depends  in  a  great  measure  the 
success  of  the  operation.  Having  reduced  the  thickness  of 
the  section  by  a  coarse  stone  or  a  tile,  transfer  it  to  a  hone  ; 
?.  few  turns  will  obliterate  scratches,  and  produce  an  even, 
•smooth  surface,  which  may  be  further  polished  by  rubbing  it 
on  a  buff-leather  strop  charged  with  putty-powder  and  water. 
"When  dry,  attach  the  polished  surface  to  the  glass  slip  :  this 
gives  a  firm  hold  of  the  section,  which  would  otherwise 
become  too  thin  to  be  held  by  the  fingers.  In  rubbing  down 
the  unfinished  surface,  take  care  that  an  equal  thickness  pre- 
vails throughout  the  section.  As  it  approaches  completion, 
recourse  must  be  frequently  had  to  the  Microscope,  in  order 
to  determine  how  much  further  it  is  necessary  to  proceed, 
a  few  turns  either  way  at  this  stage  being  sufficient  to  make 
-or  mar  the  specimen.  When  it  has  become  so  transparent 
that  objects  may  be  readily  seen  through  it,  remove  it  from 
the  hone  and  polish  it  on  the  strop.  To  detach  it  from  the 
slide  when  finished,  place  it  in  turpentine  or  ether,  both, 
being  excellent  solvents  of  balsam.  Mount  in  the  dry 
method,  by  simply  cementing  a  thin  glass  cover  over  it.  In 
recent  bone,  this  method  of  mounting,  though  the  most 
difficult,  is  decidedly  the  best  for  displaying  its  structure. 
Fossil  bone,  however,  where  the  interstices  are  filled  with 
earthy  matter,  shows  best  in  balsam. 

SPINES  OP  THE  ECHINUS  (plate  5,  figures  151,  152);  SEC- 
TIONS OF  SHELL  (plate  6,  figures  165  to  169). — These  are 
cut  and  reduced  in  the  same  manner  as  sections  of  bone ; 
but  they  require  greater  care  in  grinding,  in  consequence  of 
being  more  brittle.  The  polishing,  however,  may  be  dis- 
pensed with,  and  the  section  mounted  in  balsam. 

STONES  OF  VARIOUS  KINDS  OF  FF.UITS  (plate  8,  figure  243) 
will  well  repay  the  labour  bestowed  in  producing  good  sec- 
tions. The  gaw,  the  file,  and  the  hone  are  the  principal 


APPENDIX.  1 29 

agents  need  in  the  reduction  of  these  hard  osseous-like 
tissues.  A  perfect  section  should  have  but  one  layer  of  cells, 
which  may  be  admirably  seen  when  mounted  in  a  cell  with 
weak  spirit. 

SECTIONS  OP  WOOD  (plate  3,  figures  54  to  59). — To  make 
thin  sections  of  hard  wood  it  will  be  necessary  to  employ 
some  kind  of  cutting  machine.  There  are  several  of  these, 
more  or  less  expensive,  but  the  principle  of  construction  in 
all  is  similar.  The  wood,  after  some  prepai-ation,  and  being 
cut  to  the  requisite  length,  is  driven  by  a  mallet  into  a  brass 
cylinder,  at  the  bottom  of  which  works  a  fine  screw  with  a 
milled  head.  The  wood  is  pushed  to  the  surface  of  the  tube, 
and  to  any  degree  above  it  by  the  revolution  of  the  screw  ; 
when  a  sharp  knife,  ground  flat  on  one  side,  is  brought  with  a 
sliding  motion  in  contact  with  it.  The  slices  may  be  removed 
from  the  knife  by  a  wetted  camel-hair  pencil,  placed  in  some 
weak  spirit,  and  examined  at  leisure  ;  the  thinnest  and  most 
perfect  section  being  retained  for  mounting.  Green  wood 
previous  to  being  cut  should  be  placed  in  alchohol  and  after- 
wards in  water.  Hard  and  dry  wood  may  be  made  suffi- 
ciently soft  for  slicing  by  first  immersing  it  in  water  for  some 
days.  Sections  of  the  above  may  be  mounted  either  in 
balsam  or  fluids.  Stems  of  plants,  horny  tissues,  and  many 
other  substances  not  sufficiently  hard  to  be  ground  down, 
may  be  cut  into  slices  of  extreme  thinness  by  this  handy 
instrument.  In  order  to  obtain  a  correct  idea  of  the  struc- 
ture of  wood,  bone,  and  shell,  sections  should  be  made  in 
vertical,  transverse,  and  oblique  directions. 

CUTICLE  or  PLANTS  (plate  2,  figures  42  to  46),  HAIES 
(plate  3,  figures  74  to  88),  AND  SPIKAL  VESSELS  (plate  2, 
figures  47  to  49),  may  all  be  obtained  by  macerating  the 
leaves  and  stems  of  plants  in  water,  and  afterwards  dissect- 
ing them  with  the  needles.  Good  specimens  of  the  cuticle, 
showing  the  stomata,  may  be  often  obtained  by  simplv 
peeling  off  the  skin  with  a  sharp  knife.  Hairs  may  be  de- 
tached from  various  parts  of  a  plant  by  a  similar  process. 
Spiral  vessels  will,  however,  require  to  be  separated  by  the 
needles  from  the  surrounding  tissues.  All  delicate  vegetable 
preparations  are  best  displayed  when  mounted  in  a  cell  with 
weak  spirit. 

Cells  for  mounting  objects  in  fluid  are  generally  formed 
of  some  kind  of  varnish  upon  which  the  fluid  will  not  act ; 
gold-size  and  Brunswick  black  are  most  commonly  used. 
To  form  a  cell,  simply  charge  a  camel-hair  brush  with  the 
varnish,  and  enclose  with  a  broad  black  ring  a  small  circular 
space  on  the  centre  of  the  slide.  When  quite  dry,  it  is  ready 


130  APPENDIX. 

for  use.  Place  the  object,  with  a  small  quantity  of  fluid,  in 
the  cell ;  and  having  lightly  touched  the  edges  of  the  thin 
glass  cover  with  gold-size,  drop  it  gently  on  the  specimen ; 
the  superfluous  fluid  will  escape  over  the  sides  of  the  cell, 
and  may  be  removed  by  small  pieces  of  blotting-paper, 
taking  care,  however,  that  none  of  the  fluid  is  drawn  from 
the  interior  of  the  cell ;  in  which  case  an  air-bubble  would 
immediately  appear.  To  make  the  cell  air-tight,  gradually 
fill  up  the  angle  formed  by  the  edges  of  the  cover  with  the 
cell,  by  running  several  rims  of  varnish  round  it.  In  order 
to  prevent  the  cement  from  running  into  the  cell  and  spoiling 
the  specimen,  each  layer  should  be  dry  before  another  is 
placed  upon  it. 

The  student  should  always  have  a  stock  of  cells  on  hand 
ready  for  immediate  use.  Dozens  of  these  cells  may  be  made 
in  half  an  hour  by  an  ingenious  little  turntable,  the  inven- 
tion of  Mr.  Shadbolt,  and  which  may  be  obtained  for  a  few 
shillings. 

The  limits  of  this  little  work  have  precluded  us  from 
giving  little  more  than  general  directions  respecting  the 
permanent  preparation  of  microscopic  objects.  Our  object 
has  been  merely  to  give  a  few  plain  instructions,  which,  if 
carefully  followed,  will  enable  the  beginner  to  prepare  some 
of  the  most  popular  objects  exhibited  by  the  Microscope. 


THE   END. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 


I 


&EC  1  S  1952 

JAN  4  '58 

Ja2'58LF 

OCT 1  8  1958 
Oc8'58MS 


LD  21-100m-ll,'49(B7146sl6)476 


